People with low tolerance annoy me 
Honestly though reading posts on mumsnet these days people are getting frustrated with strangers over very little things. I posted the other day about loving period pants and someone told me I stink and am ridiculous for worrying about TSS. I've had a hard time lately (chemical pregnancy and fertility type woes) and I thought of the saying that everyone is fighting a battle you cant see. The comments didnt upset me but frustrated me, why are so many people outraged about so many things? And it's never "this irks me" its always "Rage!" - so violent and unnecessary!
I'm have a masters in English literature and it really pisses me off when people are pedantic about grammar. It reminds me of teachers who would have said "oh I dont know, CAN you?" When you asked "can I go to the bathroom" instead of may. When you can spot mistakes not everyone is as educated as you are, give them a break! Maybe they were better at something else or getting grammar right isnt important to them, who knows!
I do a lot of these annoying things - walk with takeaway coffee, talk to my dog like a child, use the other side of the petrol pump, walk at my own pace, say some of the phrases like "beautiful family" and many more. Maybe you are either annoying or annoyed and therefore I must be annoying.
It does give me anxiety that I'm being constantly judged for things and that people take things I say jokingly as serious. An example would be "cool beans" - I dont say this seriously, I'm just being lighthearted, I know it's a weird saying with no meaning, so what?
Now I sit and patiently await the crisltisism for having the audacity to have a different opinion... because that's another thing on mumsnet... very few can agree to disagree or just hear others opinions, it is a discussion forum after all.