Why is "Bye, Felicia" a racist thing?

It's not, really.

I assume you are asking this because Aaron Carter said "bye Felipe" to Tommy Solace, who took it as a racial slur and then assaulted Carter.

Solace took it mainly as disrespect, which it was, and then made the leap that disrespect was due to racism. Whatever else had been going on, Solace was already being shown the door by security when Carter threw the remark at him, so it's a fair bet he was drunk or high and misbehaving in some way. I'm not a bit more impressed with Carter, who should be old enough by now not to still be using teenager slang to insult people from onstage and consider it witty.

it shouldnt be a racist thing

It's rude and used to basically tell someone "leave, you're not wanted here", but it's not racist.

it is not. it is just said if a person doesn't care about u.

No it isn't a racist thing

Ummm, it's NOT?

The phrase "Bye, Felicia" is said to someone that you don't care about. So if someone annoying says "I'm going now" or is just being annoying in general, you'd reply with "Bye, Felicia"

I never heard that. My name is Phylicia, pronounced Felicia (always mispronounced) and I have never heard of Bye, Phylicia as a racist thing. FYI Phylicia or Felicia is an Italian name, it's just spelled different, so if people mean racist towards Italians, then sucks to be Italian.