Meaning to err greatly. Literally meaning to accidently achieve an orgasm when fooling around to get your sausage up in a girls guts. Hence, a catostrophic fuck up.
ex 1: We really can't screw the pooch in the 4th quarter, boys.
ex2: guy1-" I was so nervous with sheniqua last night that i screwed the pooch."
guy2- " ouch dude, ouch.
guy1-" ehhhh, it was good for me."