I've seen people do the dumbest things at every stage of a tournament.
Early:
Playing too wide, limping and limp-calling at high frequency.
Stacking off pre-flop way too deep, calling jams with any 2 broadways or any pocket pair 100bb deep, (even multiway).
3-betting min.
Calling ANYTHING when suited (like ANY 2 suiteds) and continuing to check-call on backdoor flush draw.
Trapping with AA or KK 100bb, 50bb deep (trapping ANYTHING worse than AA or KK at any time).
Calling large 3-bets with the bottom of an opening range.
Flat calling squeezes without closing the action (usually is a mistake).
Using ONE pre-flop range for any seat at the table.
C-betting checked flops 100% with large sizing, announcing
bluff frequency.
Limp-calling pre and donking a wet flop.
Middle:
Still trying to limp in and hit at 20bb or less.
Trying to trap with JJ, TT type hands.
Flat calling a short stack all-in with multiple large stacks still to act behind (especially with a hand like JJ or A8s).
High frequency limping with an aggressive player on left.
Limping the SB when folded to (like ... a ... FISH!).
Bubble/ICM:
STILL trying to limp and hit with less than 10bb or even less than 5bb (hell, even 2bb!! yes, seen this many times).
Limping in with a micro stack and FOLDING to flop bet (facepalm!!!)
Folding tight tight tight, praying that someone will bust before them while waiting for prime.
MASSIVE stacks refusing to call short jams or to bully isolated short stacks (come on, man).
Staunchly opening 3x or more at final table, refusing to size down to 2x for most situations.
Overvaluing A-rag when stacking off and getting dominated.
I'm sure that there are a bunch more.