As a huge fan of Top Gear I normally regard the presenters' brand of irreverence as a part of the rough and tumble that goes with having a sense of humour. I've been on the show three times and had a go at their celebrity-lap challenge, and I would love to receive a fourth invite. But I think that's unlikely once they have read this. If, however, it makes the Lads question their behaviour for a second – ambitious, I know – it will be worth it.

I normally remain below the parapet when these frenetic arguments about comedy and taste break out. But this time, I've had enough of the regular defence you tend to hear – the tired line that it's "just a laugh", a bit of "harmless fun".

Some of the Lads' comments again, in case you missed them. "Mexican cars are just going to be lazy, feckless, flatulent, overweight, leaning against a fence asleep looking at a cactus, with a blanket with a hole in the middle on as a coat" (Richard Hammond). Mexican food is "sick with cheese on it" (James May).

Jeremy Clarkson added to the mirth by suggesting that the Mexican ambassador (a certain Eduardo Medina-Mora Icaza) would be so busy sleeping he wouldn't register any outrage. (He wasn't and he did.)

OK, guys, I've got some great ideas for your next show. Jeremy, why not have James describe some kosher food as looking like "sick with cheese on it"? No? Thought not. Even better, why not describe some Islamic fundamentalists as lazy and feckless?

Feel the silence. They're all pretty well organised these days, aren't they, those groups? Better stick to those that are least problematic.

Old people? Special needs? I know – Mexicans! There aren't enough of them to be troublesome, no celebrities to be upset. And most of them are miles and miles away.

The BBC's initial mealy-mouthed apology was pitiful. It cited the more benign rivalry that exists between European nations (ah, those arrogant French, over-organised Germans), and in doing so neatly sidestepped one hugely important fact – ethnicity. All the examples it uses to legitimise this hateful rubbish are relatively prosperous countries full of white people. How about if the Lads had described Africans as lazy, feckless etc? Or Pakistanis?

What's more, this was all spouted by the presenters on one of the BBC's most successful programmes, with ratings that could only fail to impress Simon Cowell (very fast lap time). Forget the World Service; overseas, Top Gear is more frequently the public face of the BBC.

The Beeb's hand-wringing suggested tolerance of casual racism, arguably the most sinister kind. It's easy to spot the ones with the burning crosses. Besides, there is not a shred of truth in Top Gear's "comic" stereotype. I can tell you from my own experience, living in the US, Mexicans work themselves to the bone doing all the dirty thankless jobs that the white middle-class natives won't do.

What makes it worse is that the Lads wear this offensive behaviour as a badge of pride, pleased that they have annoyed those whom they regard, in another lazy stereotype, as sandal-wearing vegans with beards and no sense of humour.

Well here's some Twitter hot news: I don't have a beard, I'm not a vegan, I don't wear sandals (unless they're Birkenstocks, of course), and I have, I think, a sense of humour. I also know something about comedy. It's true there are no hard fast rules; it's often down to judgment calls. It's safe to say, though, that you can get away with saying unsayable things if it's done with some sense of culpability.

I've been fortunate enough to work with the likes of Peter Baynham, Armando Iannucci, Chris Morris, Simon Pegg, Julia Davis, Caroline Aherne, Ruth Jones, and the Mighty Boosh – some of the funniest and most innovative people in British comedy. And Rob Brydon too.

It's a diverse, eclectic group of people with one common denominator: they could all defend and justify their comedy from a moral standpoint. They are laughing at hypocrisy, human frailty, narrow-mindedness. They mock pomposity and arrogance.

If I say anything remotely racist or sexist as Alan Partridge, for example, the joke is abundantly clear. We are laughing at a lack of judgment and ignorance. With Top Gear it is three rich, middle-aged men laughing at poor Mexicans. Brave, groundbreaking stuff, eh?

There is a strong ethical dimension to the best comedy. Not only does it avoid reinforcing prejudices, it actively challenges them. Put simply, in comedy, as in life, we ought to think before we speak. This wasn't one of those occasions. In fact, the comments were about as funny as a cold sweat followed by shooting pains down the left arm. In fact, if I can borrow from the Wildean wit of Richard Hammond, the comic approach was "lazy", "feckless" and "flatulent".

Richard has his tongue so far down the back of Jeremy's trousers he could forge a career as the back end of a pantomime horse. His attempt to foster some Clarkson-like maverick status with his "edgy" humour is truly tragic. He reminds you of the squirt at school as he hangs round Clarkson the bully, as if to say, "I'm with him". Meanwhile, James May stands at the back holding their coats as they beat up the boy with the stutter.

It's not entirely their fault, of course. Part of the blame must lie with what some like to call the "postmodern" reaction to overzealous political correctness. Sometimes, it's true, things need a shakeup; orthodoxies need to be challenged. But this sort of ironic approach has been a licence for any halfwit to vent the prejudices they'd been keeping in the closet since Love Thy Neighbour was taken off the air.

Also, a factor little picked up on elsewhere in the Lads' remarks is that they do, after all, present a car show. And archaic attitudes are endemic in a lot of motoring journalism. I confess I am an avid consumer and I have to wade through a sea of lazy cliches to get to anything genuinely illuminating.

Jeremy unwittingly cast the template for this. Twenty years ago, when I bought Performance Car magazine, his column was the first I would turn to. It was slightly annoying but unfailingly funny. Since then there have been legions of pretenders who just don't pass muster. There is a kneejerk, brainless reaction to any legislation that may have a detrimental effect on their God-given right to drive cars anywhere at any speed that they consider safe. They often remind me of the National Rifle Association in the US. It's a kind of "airbags are for poofs" mentality and, far from being shocking, it's just shockingly dull.

It would be fine if it was confined to a bunch of grumpy men in bad jeans smoking Marlboros at the side of the Millbrook test track, but it's not. As I pointed out, it's the voice of one of the BBC's most successful programmes.

The Lads have this strange notion that if they are being offensive it bestows on them a kind of anti-establishment aura of coolness; in fact, like their leather jackets and jeans, it is uber-conservative (which isn't cool).

Gentlemen, I don't believe in half-criticisms and this has nothing to do with my slow lap times. But, increasingly, you each look like a middle-aged punk rocker pogoing at his niece's wedding. That would be funny if you weren't regarded by some people as role models. Big viewing figures don't give you impunity – they carry responsibility. Start showing some, tuck your shirts in, be a bit funnier and we'll pretend it all never happened.