The perfect cheerleader 'drool' movie

This had to be one of the best movies about a nerd "perving" and "drooling" over girls he can never hope to have.
The titles sequence says it all - a nerdy kid peeking guiltily through his telescope - not at the night sky - but at a gorgeous girl across the street stripping off slowly to music. Unfortunately for him he is caught by his "Mrs Bates" type mother - sexually repressed and nasty - who slaps him and promptly screws him up sexually for life!
Cut to him - many years later - now a nerdy bespectacled schoolteacher who is sexually obsessed with the cheerleaders in his class. He spends his spare time trying to peer in at the girls in the showers.
Later he manages to invent a serum that makes him go invisible and here the film really dives into sleaze and perviness - with him going invisible into the girls showers and stripping a sleeping girl naked.
Later the whole film gets really silly and becomes a slasher movie - pity - they should have kept it a sex comedy.
Its the kind of movie you feel like having a bath afterwards to wash off the "slime" - in other words I loved it!