How do you make a player feel stupid?

I got played in a really obvious way, and am upset with myself for not seeing the red flags sooner. I'm irritated because this guy is parading his new "catch" around me all the time, after he admitted he liked me and I told him eventually that I liked him too. It's getting under my skin and I just really want to teach him a lesson... it sounds petty, but I'm sick of getting treated like crap by crap guys. *Note: I didn't know he was a crap guy until this happened!*
How do you make a player feel stupid?
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