Definitions by reg the great

undie punch 

to be reamed unknowingly, usualy from behind while still wearing ones underwear. resulting in undies being stuffed into the oriface in question

i gave that bitch from starbucks a rightious undie punch..
she was all like

"AWWWWWW i say stop that young man dont punch my underwear into my date"

"captain to the bridge, there has been a royal undie punching on the lower deck"

undie punch by reg the great October 16, 2007