I don't know if I'm rarely bored or I'm so used to being bored that it's just my norm now :-s
Whatever it is, doing things, even things I end up wanting to do, raises my arousal/stress which means my irritability is a lot easier to set off.
I'm with the 'I can sit for hours with nothing around and be fine' crowd though.
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Not autistic, I think
Prone to depression
Have celiac disease
Poor motivation