Time wasters on eBay. Not as bad as the other things on this thread, but still. Especially, those with complete disregard to the fact that there are other humans involved on the other side, just like them.
Put up an auction. Got loads of interest and dozens of bids. One j*** uses a snipping tool to snatch the sale at the last second under everyone’s nose, then vanishes - doesn’t pay and ignores all messages. Due to eBay’s policy, there is no option to cancel the sale and offer the item to the next bidders until all the interest is gone and you have to start over. Happened to me a few times already.