Fucking cyclists on the road. I fucking hate them.
Also putting one small typo in a server or website file and crashing the entire fucking site and having to hunt down where the weird character is. It's especially shitty for .htaccess files. Also .htaccess code in general, what a crock of shit. I don't know many other coding languages where you can search a solution on the internet, click on a StackExchange thread, then none of those "fixed" codes work either.
Also when I forget to clear the cache, so when I fix code, it appears to still be broken for no reason whatsoever.
Coding isn't my career but I have to do it from time to time, and when I do it usually causes a lot of anger.
OH and you want to know what makes me REALLLLLY angry. Sounds outside my window while I'm tired and trying to sleep. Dog barking early in the morning, birds chirping. It's so bad that I wear earphones to sleep because I'm such a light sleeper and can't sleep through any sound at all.