I walked out of my class as they attempted to sing happy birthday to me
Why don't you like people singing happy birthday for you?
I just hate the practice of singing happy birthday to people.
You may not like it when people sing Happy Birthday to you, but not accepting your classes' gesture of love is inconsiderate. Consider how other people feel before you blow them off.
Just because you like it doesn't mean I have to.
I'm not saying you have to like it, but your friends were trying to do something nice for you and you shouldn't walk out on that.