A jerk of a guy who has little to no self control or common sense. He is completely inept in every way. He is an unattractive guy, crass and ignorant. A Kevin is a disloyal sort, if given the chance he will turn on you like a rabid dog. Don't ever trust a Kevin. He will take you for everything he can, use you up and toss you aside.
Kevin is an ugly guy with a bad attitude, avoid him like the plague.