Well I’ll share my own (unwitting) DYKWIA experience then...
Arrived a wee bit early for a flight from LIN, had a bag to check so went to do so...
Only one desk open, longish economy queue, but a clearly-signed priority entrance too (with no-one in it). I walked straight into the priority bit... as I stood waiting I had several people from the economy queue shout over that they had been waiting for ages etc. I replied that this was the priority queue. When the person in front moved, I politely, but loudly asked the check in person (before stepping up) if the priority line was in operation, to which I got a yes....
Stepped up feeling righteous (and the daggers in my back), handed over my passport, put my bag on the scales... only to be told that they can only check bags in 2 hours in advance and I needed to come back in 20 minutes!
I reclaimed my bag and sloped off without a glance behind me!!!