I'm irritated by my friend, particularly when we're around others, she has a very mocking and condescending sense of humor, as such she is irritating to be around at times.
Why do you feel irritated when you're around others with your friend?
Because my friend bothers lots of people.
She shouldn't do that. That's a rude thing to do and you should let her know how her behaviors are affecting others. Talk to her to make here aware of her actions.
I just don't understand her sense of humor.
It sounds like she isn't a very good friend then. I think you should cut ties, since the relationship isn't making you happy. It is okay to break up with toxic friends, let her know how her rudeness make you feel and say goodbye politely.