After the offending reporter leaned in for a smooch, Smith pushed him away, saying, "What the hell is your problem, buddy?" He then reached over to shove him. As he moved on down the red carpet, Smith told the next reporter, "Sorry! He tried to kiss me in my mouth! This joker is lucky I [didn't] sucker-punch him."
For further inspection, here's the kerfuffle from two different angles:
I wonder why Will is so sensitive about a man showing him some affection? Oh yeah: