Some things just bother the heck out of me. Right up there with global thermonuclear war and bumper-to-bumper traffic has gotta be counting out of rhythm. I don't know why it bothers me so much, but I have an almost visceral reaction to it.
The worst offenders for me are large sporting events. At some point, there is always an audience clap-along with a song. For some unbeknownst reason, large crowds will inevitably speed up to faster than the actual rhythm, falling into a vicious feedback cycle that pushes them more and more off-beat. It's a curious phenomenon, because wisdom of the crowds says that they should average out to the actual beat.
In any case, eventually they fall so far off that they either lose an entire beat, or the arrow of time has mercy on their poor out-of-rhythm collective consciousness and shifts forward, allowing them to perfectly align with just one beat before again jumping ahead of the rhythm. I'm usually the lone holdout, clapping along to the actual rhythm while people give me the "are you retarded?" look.
Sometimes I think that I'm the one without a sense of rhythm, since the majority stays together. But then I look at the majority - the average intelligence, average weight, average musical ability, average everything - and realize that I'd rather be an outlier. All I get for staying on beat are dirty looks? I can live with that.