The current one about the Easter eggs as a party bag gift has opened my eyes.
Some posts down the thread (not that long) it becomes clear that the OP is not criticising a party bag she has received, but canvassing opinions for a party she is about to give.
Yet post after post repetitively slams her for being ungrateful/critical/getting her timings wrong (no it is not yet 3 weeks after Easter, but will be by the time her DC's party happens, people!) etc. etc.
That thread's not about anything sensitive and I imagine the OP is unbothered. But if people are generally posting on AIBU without actually reading/understanding what's been said, then their opinions are pretty worthless (though nonetheless strongly expressed). Perhaps we need an emoticon for 'No idea what this is about but thought I'd shout my random prejudices anyway'.
So, go on, AIBU? (feel free to mention if you've read this or not :) )