Pretty much everything already said by previous posters.
The vacuous brain-dead that are touted as "celebrities" now, purely based on their willingness to strip down to a teeny bikini or man-thong on camera.
Smug yet vitriolic vegans - you know the ones. The ones who tell you how much good they're doing for the planet by eating their imported avocados from Chilli and pineapples from Peru, alongside their New Zealand apples and South African oranges(nice carbon footprint, you steaming pile of shit) whilst filling their facebook page with photos of abbatoirs and animals "suffering so you can eat meat".
Children. Dirty, smelly, revolting little packages of snot, shit, excessive noise, piss and vomit. Yes, I do appreciate the irony of saying this whilst being on Mumsnet, and having several of the environmental disasters in my life.
Tourists. The next time I find fucking tourists in my back garden on my bench eating ice cream from the cafe near me, I will take a spade to them. Or a hoe. Whichever is closest to hand. I am TIRED of chasing people who have no right to be in my garden out of my garden. Have some fucking manners.
Crowded pavements and that group that insists on walking four or five abreast, forcing others off the pavement. I am VERY confrontational with people like that. The elbows go up and if they walk at me, they walk right into my elbow.
I've been a grumpy old cow for at least 20 years now and I believe I've honed it almost to perfection.