To beat utterly and completely at something (including and especially life in general).
To get shitslammed:
To perform
extremely poorly on a test. To get beaten badly at a
videogame/sport/etc. Basically, to be completely
overwhelmed by something.
"I thought I was going to do well on that test, but I just got shitslammed."
"I tried to send my
knights around to
trample his archers, but they got shitslammed by his
pikemen before they could ride ten feet."
"Shitslam that guy!"