When your watching an engrossing movie or documentary etc and right at the crucial point,where the most important thing is being reveled ,some loud noise,or somebody comes a talks to you,drowning it out so you don't hear what was said.
Laser printers that run out of ink midway through a print job, or you don't have enough paper to complete a print job.
Mobile phones when they run out of charge just as you answer a call.
Trying to adjust gearing that is slipping on a 3 flywheel bicycle,and every adjustment you make just makes things worse.
Group photos where your the only one that suffers red eye.
Women who constantly overload washing machines causing them to break,then getting the monster of a unit out and back again after you repaired it for the umpteenth time.
People who lend your property out without telling you, to people you have never met.
Treading on LEGO with bare feet
Builders/workmen who start using the nosiest machinery possible at the crack of dawn