I don't bore easily, I in fact probably qualify as "easily amused", but I can get bored.
Usually though it has something to do with being sick in some way, so that I can't do the things (or even think the things) that would keep me out of boredom. The most bored I've ever been in my life was when I was delirious. During the parts of it that I can actually remember (and there are a lot of gaps for obvious reasons), I was bored out of my skull while at the same time disoriented and hallucinating and in pain and puking and unable to think straight, it's just that it felt like it would never end and that was where the boredom came from.
It's usually situations like that that bore me. Things where I'm really sick and can't even alleviate boredom in the normal ways because my brain won't work right to do it. The rest of the time I'm mostly fine (with a few exceptions). Also some medications can make me bored for the same reason being sick can.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams