NSFW; What makes guys uncomfortable?

My [guy] friend and I were playing this game where one player sits down (or stands up) and the other tries to make you uncomfortable by doing things to you and I was the “victim” in this situation. My friend had to leave before I could try anything weird but I didn’t know what to do to make him feel uncomfortable. We’re planning on hanging out and playing this game again sometime this weekend, and I have no ideas, still, of what {sexual} things make guys uncomfortable. He claims to be the “All-Time Winner” of the game, and I want to prove him wrong.
What sexualish things can I do to make him want to make me stop? (That’s the point of the game; do something sexual to make the other person uncomfortable so they’d give up and the other person would win the game)