As per the title - what things make you want to have a really unreasonable rant?
For me, it's the behaviour of some people at work around one of the doors in our office. I work in a secure office, which means you need swipe cards to get in, and have to push a button to get out. To get into any of the working areas, you have to go through at least two of these secure doors. They remodelled the office not too long ago and put an extra door in - as a result, there is a door which used to be secure but doesn't need to be any more.
It still has it's swipe card reader and push button, but they're not switched on. Some people haven't realised they're not switched on, however, so still swipe or push the button. As I know you no longer have to swipe, I don't bother, but just walk towards the door and open it as normal - but if one of these people is there, I see them scramble to swipe their card for me (which would be a breach of security if I needed to swipe to get through this particular door) or push the button, while giving me evil looks for making them open the door for me.
I get rather annoyed at this, but realise that this is not reasonable - after all, they think they're doing me a favour. I just imagine that they're thinkin I'm a lazy ungrateful cow as I make them open the door for me every time...