Tell him you have a boyfriend or you’re married
While that may or may not be true, he’ll feel like he lost and give up.

Tell him you’re gay or bisexual
He’ll expect it’s not him you want.

Go workout, get soaked in sweat and forget to shower afterwards
Having to smell your natural odors will definitely turn him off.

Get drunk and text him something stupid
He’ll question your intelligence.

Have sex with the person he hates
How could you? It’s worse than cheating though you’re not in a relationship.

Display interest in someone else
Competition? Nah.

Be obnoxious and rude as hell
When in doubt be the worst possible version of yourself. If that doesn’t work, he obviously is a robot or alien.