Killer Nerd (1991) on Netflix

A nerd is harassed by punks, and is the object of ridicule at work. Enamoured by a co-worker, he buys a tape series on how to be cool, summons up his nerve, and goes to the co-worker's house, only to find her in the clutches of another co-worker. Dejected, he goes out on the town and parties with some babes, but when their friends, who turn out to be the same punks that harassed him earlier, trash him again something snaps, and the irritants in his life begin experiencing an attrition problem.