A Midvale business owner says she was "gobsmacked" by security footage showing a man dressed in women's clothing committing a lewd act, then defecating, wiping his backside and tossing toilet paper away in a car park.

Footage of the incident - posted on the Perth Have A Whinge Facebook page - shows the man, who appears to be wearing a bra and high heels, climbing into a white utility before he strips off and apparently starts pleasuring himself.

The events transpired outside the WA Salon Supplies business and security cameras were triggered when the man drove around the back of a Caltex service station.

Footage viewed by WAtoday shows the bespectacled man seeming to defecate, then reach for the toilet paper - a used portion of which he then casually tosses away.