The act of having intercourse with a female. Unlike regular sex or "punishin it", if you "pack it" you're bringing a whole new element into the game in that your shit hot (having plenty of experience) having sex and you don't quit until you say it's over. Additional you prefer to to go deep from the get go and you don't fuck around.
Bro 1 - Hey son what when you get back Tiff said she can't wait to get at you.
Bro 2 - Dayum I can't wait to get home and PACK IT booiiiii!!!!
Chick 1 - Hey girl I heard you got with Luis last night.
Chick 2 - Hell yeah he was packing it hard.