What is your worst salt/suss moment you have experienced yourself or against an opponent?

I was curious to know what other players have experienced themselves or against opponents in tournaments (or casually?). No one likes losing and rules can be misinterpreted and communication can get mixed up.

The worst one I've experienced so far was at a Teams Tournament against a Guard Player. I had destroyed 2 out of 3 of their Rogal Dorn Commander tanks and was on the verge of tabling my opponent. In a last ditch effort, they attempted to use the antenna of their last Rogal Dorn Commander to peak over a ruin wall to shoot one of units. I checked the visibility at eye level and stated that I did not believe he could see over the wall. He agreed - Then he replaced that Rogal Dorn Commander with one of the destroyed models which had a higher antenna. I was baffled as I knew this was not legal but I let it go as I knew this interaction wouldn't have made any difference to the result.

P.S. Please follow Rule 3, no direct callouts!