Very annoying are no shows, especially when you turn another appointment down for theirs. I used to call them after 5 mins over & either leave a voicemail or text "are you OK finding me".
I sent one on a wild goose chase once, made him wait 10 mins because I'd "gone to get something out of the car" sent him to 2 different hotel rooms "oh you miss heard me, it's room 123 not 124" it made me smile, the fool still didn't get it after going to the second room. I bet he thought twice before wasting someone else's time again..