When you throw your fist in the air in an excited/victorious manner, often accompanied by a lunge of the body.
Liz walked out of saturday detention and gave a little jump as she fistpumped the air, 80s style.
(noun): the type of douchesbag seen in public- particularly nightclubs and beaches- reminiscent of "The Jersey Shore". Characterized by medically disturbing tans, overly-producted hair, and under-sized Affliction T-shirts. Often observed performing a simplistic, repetitive motion, also referred to as a "fistpump ".
"Whoa! This place is full of Fistpumps tonight. Is there a MTV casting call or something?"
Also used as a replacement for other derogatory names, i.e.:
"Quit being such a Fistpump! " or,
" Let's play smear the Fistpump! " or,
" Man, fuck you, Fistpumpa! "