Suddenly discovering they had a significantly different social view about something that was important to me.

rude to the help

Treating a waiter badly. They have a tough job and if they aren't perfect it's understandable.

Arrogance

Deceit

anonymouslyyours she already had a boyfriend was not too fob me off it was true as me and somebody i worked with ear wigged what she and her boyfriend got up too

Same. I don’t like cruel people. That puts me right off.

Being mean to their friends

Drugs

Specifically, once, it was when a man I was briefly involved with, rather loudly went off about "that faggot"...just because I went over to talk to a friend in a public place we were at. It was horrifying to me, and the end of my attraction.
In general, intentional cruelty or abusive behavior towards any other beings, pretty much dissolves any "crush" feelings I've had for someone.

I found out she has a fu*k buddy.