How to get him
Hide his glasses. When he confuses you with Shampoo, just humour him.

Competition
If you follow the advice above you shouldn't have much trouble with Shampoo. Unless, of course, she suddenly wakes up one day and thinks "Screw chinese amazon law! Shampoo love stupid duck boy!".

He likes you if...
He goes psychotic whenever you're interested in a guy or whenever a guy is interested in you. He'll also be willing to totally humiliate himself for you at the drop of a hat.