In my experience, if somebody is being rude to you and not respecting your space, feelings, or you as a person and asking them nicely doesn't solve things and avoiding them isn't an option, then telling them in a not so nice way so they get the hint that they're crossing a line is the only viable alternative.

I used to be a very naive kid who let people walk all over him because I was too afraid to stand up to people. Me being that way has caused me more pain than I care to admit. When I finally had enough and grew a pair and made it clear that I'm not a soft target who can be so easily messed with anymore, people finally learned to give me my space and leave me the hell alone because I meant business.

Sometimes, one needs to take a stand and be bold in life to get their needs met.