The ones that really get my goat are the groups that (take up the whole trail and) look behind, see me/us bearing down on them (albeit at a respectable speed at this point), and simply turn around and continue on their merry way without even stepping aside one inch.
I mean, WTF is it with these people? Fair enough they might have had issues with MTBers in the past, but don't be so f&*^ing ignorant as to label us all like that. Or maybe they're just ar5eholes.
And another bugbear of mine is MTBers that let their dogs loose on singletrack trails. This happened again at Swinley on Saturday – bloke pulls aside to let me past, then 50m on his dog leaps out in front of me and I have to hit the anchors big time. Whoever you are your dog could've caused a stack AND been injured in the process. Sort it out FFS. This is the main reason that whenever I go running with our dog, we stick to fire roads and other trails where I know he's going to be safest, i.e he's not going to ambush bikers and they're not going to do the same to him.
Rant over.