Sometimes I worry that I'm too quick to suspect people's motives. I blame politicians. They so desperately want voters to like what they say that it becomes impossible for a contrarian like me to do so. I can't even hear what they're actually saying. However clearly their message is being conveyed, however eye- or ear-catching their rhetoric, all I'm aware of is the eagerness to please, the meretricious reaching out to a useful demographic.

For example, here's something the transport secretary Patrick McLoughlin said last week about road signs: "Ugly and unnecessary signs clutter up the network. New signs seem to sprout like weeds, without any apparent consideration of what's already there… Near me in Derbyshire there's an ugly big sign by a beautiful medieval church that just says: No Footpath. It's on a small country lane. Of course there isn't a path. We don't need a huge sign to tell us that. So I'm determined to do more to sort this out."

Is that perfectly reasonable? I think it might be. It's not the most pressing issue facing government but governments can do more than one thing at a time. Politics isn't short-staffed. I was quick enough to scoff when ministers cited the fact that most people are more worried about the economy as an excuse for shelving gay marriage. So, to be consistent, I must accept that it's perfectly reasonable still to want to sort out unnecessary and ugly signage even when Syria's having a civil war and the eurozone's in recession.

Still, I hated it. He made the remarks in a speech to a Campaign To Protect Rural England conference and, when I read them, all I could hear was the subtext: "I wish to shore up a section of the Tory vote by crowd-pleasingly joining in with your grumbles." But I accept that's not mutually exclusive with his also genuinely thinking that there are lots of unnecessary road signs. Maybe he feels that more strongly than I give him credit for. Maybe he's barely aware of the vote-securing appeal of his remarks. Maybe his is an honest, modest goal that more megalomaniacal politicians could learn from. "I know I'll never sort out the Middle East," he's saying, "but I can at least bring some common sense to the UK's road signage system."

However, I think he lost his head a bit later on in the speech when he said: "My message to highways engineers is: if in doubt, don't do it." I'm not sure that's the right approach to the provision of road signs. Doubt is the presiding emotion whenever a safety sign is installed. Nobody thinks the alert is definitely required, that the disaster being warned of will certainly come to pass, or the road would be closed. Any "watch out for this crumbly cliff/ startled deer/ emerging elderly couple" signs are always put up in considerable doubt as to whether the promised rockfall, stag or wizened duo is going to turn up at the right time to terrify a car.

I also found myself sceptical of the goodwill of the two MPs who represent the constituencies bordering Nadine Dorries's. Andrew Selous and Alistair Burt both offered their services to Dorries's constituents last week, should they find themselves in need of an MP while she's away appearing on I'm a Celebrity… Get Me Out of Here!. They're jostling to be "supply MPs" for the people of Mid Bedfordshire. A perfectly nice and constructive gesture, you might think. You might be right but I can't think it. Too poisoned by suspicion, I was repelled by what I assumed was a mixture of self-publicity and self-importance.

The self-publicity is obvious. "We're still here!" they're boasting. "Yes, we're both still getting on with vitally important constituency business. We haven't jetted off anywhere to eat balls." It just seems so opportunistic and swotty. Do they really think they seem helpful by saying that? Are they stupid enough to believe that will make people like them? Perhaps not – in which case, maybe they're just being sincere.

I detected the self-importance in their assumption that ordinary constituents need their MPs for anything on a day-to-day basis – as if there were jobs, like notarising wills or unblocking sinks or transubstantiating wine, that only an MP can do. I know people are exhorted to write to their MP about problems but it never seriously occurred to me that it did much good. MPs have the wrong sort of power. What are they supposed to do if you're out of work or have noisy neighbours or don't want a betting shop opening at the end of your road? Table a private member's bill? Or just write to the minister concerned to justify their publicly funded headed notepaper?

The irony is that Nadine Dorries, for all her fame-seeking vanity, is basically right that having a month off to bicker with Brian Conley over the dunny rota probably won't make much difference. Still, she's taking the piss in more ways than one: "I'm doing the show because 16 million people watch it. Rather than MPs talking to other MPs about issues in parliament, I think MPs should be going to where people go," she said in justification of her actions. Not only does she denigrate the entire process of parliamentary democracy, and propose its replacement by a modern-day Colosseum, she also has the cheek to criticise her parliamentary colleagues for not going to the jungle themselves.

All this motive-suspecting left me in a contemptuous mood when I heard about Armstrong the Good Giraffe. He lives in Dundee and isn't really a giraffe – he just dresses as one. However, he is, or at least he claims to be, good. He hitchhikes around Scotland doing benevolent deeds such as handing out free bananas and picking up litter. He's unemployed but bankrolls his philanthropy by busking.

Well, you can imagine how suspicious this made me. "He must be running for mayor," I thought, "or using it as cover for a series of murders, or to lull people into a false sense of security before blowing up the Queen while collecting an MBE." Our society of spin doctors targeting the roadsign-sceptic demographic and Nadine Dorries forsaking the House of Commons for a coffin full of roaches has left me mistrustful of the genuine goodwill of an eccentric Scotsman reaching out to his fellow humans by disguising himself as an animal.

Nevertheless, somewhere deep inside, I hope he really is a good giraffe. And not just stage one of a guerrilla marketing campaign for Toys R Us.

David Mitchell's autobiography, Back Story, is out now