[Yung Lean]

If programming/coding then bugs that you spend weeks to fix.
IT related like PCs, Laptops so on. = Annoying wrong unsatisfied clients that try to explain you what you did wrong when eventually you know what's going on but their too dumb to understand.
As @pvnk said in his list the co-workers... sometimes you can have really crap co-workers in some places co-workers are the best. Depends where you get in to.