Walking up to a yard with one tree you bid on as an one hour removal, and having three more customers scheduled for that day...the one removal turns into a four day ordeal of multiple trims, removals, and basic whole yard overhaul. Then dealing with the other three customers who were expecting you.
Hearing countless stories from customers about their "amazing" removals they did for friends or relatives. Yet they hire you for a notch-and-drop (ten minute job).
Asking for a chainsaw and somebody hands you a piece of Stihl junk instead.
Broken recoil ropes at 75 feet from the ground.
Assisting another tree trimmer who cannot tie a bowline.
Having another tree trimmer beg you for help rigging down a tree, only to arrive at a job you had bid on yourself, and did not want the job then. But you owe the other tree guy a favor, so you do it...(for half the price you were going to charge the homeowner)
vines...locusts...plums
Arrogant arborists who complain about your style of trimming, but will plant non-native species of trees in customer's yards. You would think people would have learned something from dandelions, buckthorns, and other invasive species by now.
One thing that never pisses me off is my groundman. I trained him...if he's at fault its my mistake.