Moon-walking praetorian and scion, though that was probably a glitch cause they couldn't turn around in one of the ghost buildings right and I'd snuck up behind them.
But, dumbest things I saw yesterday was a asari valkirye at level twenty with only tech armor and warp(why no human adept at that point?).
A kroguard with a geth smg, no equipment and a grenade and assault rifle perm.gear.(assume he was doing it for challenge or something.)
The backwards Praetorian sync kill
And a vanguard trying to carry the package, charging, and running back to grab the package yelling "I'm carrying it, don't pick it up!". Every few steps was the same thing; Charge, tell me not to pick up the package, run over, pick it up, charge another enemy.