M$ Patches/S Packs/Whatever that require a reboot (PITA #1) and then assume you want to reboot immediately (PITA # 2) without giving you any further choice - as you say, usually when you have something else on the go (hey, we're multi-tasking, right?). So you leave the dialogue with the single button "Reboot" displayed on the desk and get a coffee while you wait for the other task to complete, and your helpful, well meaning colleague presses the button for you while you are at the machine (PITA #3)

The worst part about #3 is the fact that you are partly responsible, but it doesn't stop you feeling as if you want to flay your mate alive and nuke Redmond all the same