1. slang To complain or gripe very intensely or incessantly about someone or something. We've been ragging about this issue for so long that it's a huge relief to find out they're actually going to fix it! Instead of just ragging about your annoying coworker, why don't you actually try to resolve the issue with them?
2. slang To tease, mock, or annoy someone about some issue or thing. In this usage, a noun or pronoun is used between "rag" and "out." My friends are always ragging me about my pink backpack, but I quite like it. OK, Tom, stop ragging Sally about her new boyfriend. You've embarrassed her enough already.
See also: rag