The guy who sets up his stall in the toilet of a bar/club - he is usually built like a brick shithouse - and then demands money with menaces for even having breathed his air. In most cases he dispenses soap and paper towels by invading your space and foisting it upon you, then glowers at you as you say thanks and don't pay. Using their range of aftershaves is ill-advised and costly, and why anyone would buy a lolly from a guy they met in the toilet is beyond comprehension. Attempts to avoid the bog troll often result in loud verbal abuse about your personal hygiene.
Bog trolls might be excused their actions on the grounds that sitting in the toilet for five hours a night can't bring a lot of job satisfaction, except that it's not a proper job and no one wants them there in the first place.
Bog troll: Soap, paper towel?
Me: No thank you, I can manage to do this by myself.
Bog troll: (indicates tray with assorted change from previous mugs) Fair enough (looks at you like he might have already killed your family)
Drunken reveller A: Taxi home?
Drunken reveller B: Nah man, let's walk. I broke the seal too early and spent a tenner on bog trolls already.