The Hexagon Brothers in Pokémon XD always make me laugh ridiculously hard when they appear and try a count off on who is present.
http://www.youtube.com/watch?feature...8yfAG6Y#t=227s < Direct link to 3:48...
Gets me every single time, especially later when they re-appear and count off properly!
But yes, there are certain random trainers who stick in peoples minds... Joey, Shorts guy, Old Man, Earl (The teacher dude), the Magma/Aqua grunts etc... There is some quality ones... OH the foreign team rocket guy who we rediscover in Unova!