It's not gramatically correct, and I don't think a native speaker would say that, even if it were fixed. It comes across as somewhat rude, but not particularly forceful because of the question. If someone was annoyed enough to call someone out for being selfish, he probably wouldn't phrase it in such a way.
First of all, to fix up the grammar, one would say, "You're selfish, aren't you?" The extra "a" in there is extraneous.
But, as I said before, phrasing this as a question sends mixed signals. You're showing your annoyance by calling someone selfish, but weakening your statement by turning it into a question. In real-life, a person would probably say something like "You're selfish," or "You're being selfish," or "Why are you so selfish?" But he wouldn't put the "aren't you?" part at the end.