I've been lucky, only had three really bad non-revs in the last six years; once every two years, not a bad average. I'll just list the top two....
Number one was an vacations employee that I was ticketing PHX-SAN at the counter, first got upset when I wouldn't move her niece up to SA1P with them since she is only on a buddy pass and not an eligible family member. Then she got upset when after getting all the ticketing done it was too late to check their bags. She kept screaming about how long she'd work for HP and how she knows that rules and I don't and hen she threw pencils at me. It was so bad that other tkt cntr agents documented her pnr and the tkt cntr manager could hear hear all the way back in her office. Surprisingly they made the flight which kinda bummed me - I didn't find out till a few days later that while they were in flight, the MOD was on the phone with the pass office; her benefits were pulled before she even landed! Called up the pnr the day after her skd return, turns out she threw such a fit when she tried to check in on her return and found out she was not eligible to fly that they had to call the cops on her and had her hauled off!
Number two was a SA7P that had been trying to go PHX-MSP. I was working the last flight of the day and luckily all the non-revs got seats before boarding began 🙂 During boarding I get a call from the tower that they need an agent on board for an issue. I get down, turns out this 7P had parked herself in f/c and wouldn't move when the F/A asked her to. She said she deserved to be there since she had to wait 9 hours to get a seat. It got to the point to were I had to flat out tell here that the plane will not move until she does. Finally she gets up and starts to move back when she mumbles something about "how she ought to slap that f*&@ing F/A." Well that was not the thing she should have said. I told her to turn around and march right off the plane and she was no longer welcome to fly with HP. She said I didn't have the power to do that, well the Captain over heard and said "Well you might think he doesn't, but I sure as hell do, now get off my damn plane!" She just sulked right off, up the jetway and left the boarding area. We canceled the ticket, marked it for refund only and turns out the both the Capt and the FA filed with the pass office and I got a a very nice thank you basket from the crew.