Mine was when the DPE pulled the landing gear motor C/B and the gear light C/B during initial rotation, I went out, shot the DME ARC, did a spanky VOR approach and the gear never went down.
His beef? "You needed to look into the mirror to CONFIRM that the gear retracted" despite the fact that I was under the hood.
Seemed a little "We're gonna show that Riddle student since they went self-examining and I've lost 99% of my business but there's a couple stragglers to pick on to prove my point to the local FSDO" but I kept it positive, did some "retraining" and used a different DPE for my retest.
I still hate that guy!