Sitting down to a short viewing of TV, (perhaps while eating/waiting to leave) seeing what's on to pass the time and every sodding channel being on an advert break at exactly the same time

You'd think one or two would want to stagger their ad breaks to pick up idle viewers....
(ABC1 used to be good for this)
That, and humans basic selfishness that governs every single thing they do.....but that's a side issue.
*Edit* Though now i've read through this thread I'm reminded of something I fall afoul of constantly.
People who have personal fury points about trivial matters, but don't tell you what pisses them off or not until you've already blundered over their personal rage line.
Everyone's little fallacies are personal to them, be they grammar, habitual, etiquette or whatever.
If you don't inform someone about something that intensely annoys you, then they go and do it, infuriating you, that's YOUR fault, not theirs.
Fair enough if they know its something that annoys you then they carry on doing it, that's a whole separate area, but people seem to assume everyone else is psychic to their wants and needs and is doing it personally to piss them off when it could just be an innocent mistake.
This also applies to employers/bosses who train their staff badly then blame THEM for making mistakes/not following proper procedure.
I'm falling afoul of this a lot recently. If I wasn't instructed on how to do a task to yours and company standards (which are usually two separate things in themselves) then it's not my fault when I mess it up, is it?
Also Tweetdeck, which used to be sooooo great then Twitter bought it out and seemingly hobbled it, made it so you couldn't download it, took off the spellchecker (why?) and removed the ability to see follower counts in peoples tweets amid other pointless changes that made it worse.