Flipping someone off could be disorderly conduct. (Flipping off a cop is NOT disorderly conduct per a specific case.)
As far as the gun, I can see that if it was done in certain ways, it could scare the hell out of someone and if that happened, it could be illegal. The question is whether someone is put in fear of serious bodily injury or death, and if the gun looks real, then they could easily feel that way.
