This is not something I have ever done, or considered doing or seen happen - but why ask if you're gay after stating you are not?
Unless you find men sexually, mentally, and physically attractive then of course you are not gay.
personally, I would not kiss a friend on the lips whether male or female quite frankly because I'm not in any way an affectionate person. I'm quite happy with an 'alright' when meeting up with a mate. Hell, I'd be like that with my own Mother if I hadn't seen her for a year. lol.
Don't feel uncomfortable doing it, it's just I don't feel the need for it.
Only person to ever seen my affection is my wife, and it was the 1st time I'd seen it myself that day too. !! haha