Crappy TV adverts.
Darts players who look towards the camera like they've done something amazing. Mate, you've thrown pointy things at a BOARD, you haven't run the London Marathon!
People who don't indicate at roundabouts.
Reality TV contenders who try to use their appearance on a show as a short-cut to fame.
People who speed up their car on their way to a junction, then brake sharply when they get there.
People who drop litter on the ground despite the fact there is a bin close to hand.
People who can't control their dogs, I can't think of the number of times when out running that I have nearly tripped over some bloody dog!
This is great, salem. You've used a Britishism in nearly every example you've cited! I love it!

There are a couple that I was unfamiliar with (in bold, below), or just never paid enough attention to before to have it stand out to me:
1) "People who don't
indicate at roundabouts."
"People who don't indicate
what at roundabouts?" I wanted to say.

Americanisms are much less interesting, I think. We would say: "People who don't signal at traffic-circles". How dull. I, personally, prefer "roundabout" to traffic-circle (both as a manner of speech and as a traffic-flow method: we only have a few on the Island and they make things so less annoying). The term "roundabout" just sounds quaint, whereas "traffic-circle" sounds like a bureaucrat described exactly what his soul-less existence saw.
(by the way, I also find that annoying, but I would expand it to say "People who don't use their signals, EVER"

2)"People who speed up their car on their way to a
junction, then brake sharply when they get there."
Yeah, I was unaware of use of "junction" instead of "intersection". Americans use "junction" for where roads meet on a map, usually, or in directions on a traffic sign: "Junction 495, 3 miles". That sort of thing. But then, most of you already know this, of course.

I believe Mr. Churchill noted that we are one people, divided by a common language.
I thought it was Patton.
Actually, some do attribute it to Churchill, 'though George Bernard Shaw and Oscar Wilde are also often cited.