When some asshole tries to cut in front of a longline of cars and the cars stay strong and refuse to let said car in. Then many of the motorists "flip the bird" to said asshole.
That idiot tried to cut in at the front and became a bird watcher when all the cars went by and flipped him off.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.