true story, ive been arrested for cussing at a cop. i spent a night in jail for that, charged me with interference with official acts. the judge laughed and said
"i guess you cant cuss at cops now" then dropped the charges with the quickness.
thats probably exactly what would happen if you flipped off most cops, they'd arrest you on some petty charge, you get to spend a night in jail and get charges dropped with the quickness. maybe even set up a nice lawsuit if something happens