Unless I knew the pilot who flipped me the bird I would be ****ed. With my Captains permission I would ask ground for their tail# and send a letter to their chief pilot asking for a clarification of said offense and an apology from the offender.

I don't fly 121 so maybe you guys think I am overreacting but I think that is totally unprofessional. What would you Captains do if you saw your FO do that? Actually, I am assuming it was NOT the CA that flipped you the bird.