So I did a stupid thing a couple of weeks ago, but the only thing damaged was my pride.
I was visiting a friend in upstate NY, and we were discussing where to fuel up before the 300+ mile trip home. He was a former TDI owner, and mentioned that one of the stations even had off road diesel. Well, I ended up going to that station, and pulled up to a pump with two diesel hoses. One had a full-size nozzle, and the other had the leaded-size nozzle needed to fit my TDI. That was labeled #2 Diesel (OK, it's all the same) but the price wasn't visible. I did note the standard and off-road labels on the pump, but it noted that off-road required going inside, no pay at the pump.
You probably know what happened. I ran my card, pushed the button for the hose that would fit, and started pumping. I figured since the pump started that all was fine, but after about 3 gallons decided to check. Yep, I was pumping nice red-dyed fuel into my car
Stopped pumping, complained inside that their pump wasn't well labeled, and figured I'd finish filling up somewhere else. As I was leaving I pulled to the other side of the pump, where (a) the off-road button clearly said off-road (not #2) and the correct hose had the correct nozzle. Put in about 10 gallons, and figured that at least I had the pair of receipts showing that it was an honest mistake. Note that the off-road was only 5 cents cheaper.
I did end up changing the fuel filter a couple of days ago (it was time for the periodic 20k change) and there was no sign of red. And next time I visit him I know which side of the pump to use
(Edited for typos)