I really need to go back and watch more TNG to see if my memory really matches reality, but when the "TNG cast is clique-ish" argument comes up, I really think it's centered mostly around Riker. If you're not part of his circle of friends, he really does treat people very differently.
For a female romantic interest, that smile you talk about takes on this weird look that I can only describe as ... "Oh, yes, you will be mine, you just don't know it yet." If he feels threatened in any way by other officers, he seems to throw all decorum out the window and get downright petulant. Jericho, Shelby, Tom Riker, and Ensign Ro all come to mind there, though he does soften towards her later after Conundrum.
Riker can indeed be a real ass to people who are different