I think I have a psychic gift and if I tell anyone about it I'm afraid they think I have schizophrenia.
What is this psychic talent you have?
I can tell when someone is thinking bad thoughts about you
It is great to have new talents but you're right to be worried that people will think that you are weird. You can find people and talk to them about it until you feel better about your new talent and maybe then you can share it with people you trust.
I will tell a co-worker soon but I need to make something up first.
I would be careful to not sound like you are a believer in the paranormal, as this is justifiably off-putting to many people.  It is likely that you have a brilliant, natural talent for reading other people's emotions and body language.  Just talk to someone about it, get a better understanding, and then you can tell others when you have a feeling about someone's inner thoughts.