Am I being jealous or is my concern justified?

My gf has friends on facebook. Each time she makes a random statement, one of her male friends always replies. The fact that he always replies irks me slightly. What really gets me is that this dude is always replying with some sexually suggestive comment. He doesn’t hit on her directly but he keeps talking about stuff like naked twister or being naked or nudity. Every time!

Was I right in telling my gf to put the brakes on him before I have to comment on facebook and things really get blown out of proportion?

I feel my gf should have put an abrupt stop to his comments without me telling her to do so.