When you are talking on some form of chat, (messenger, icq, talk, chatroom etc) and you accidentally hit the caps-lock key and don't notice before sending the message. (Caps in chat means that you are shouting)
Analogous to how someone with Tourette's syndrome will randomly yell (and often swear) in the middle of what they are saying.
Sally: Hey how are you?
Tom: I am good.
Tom: Have you heard about JAMES'S NEW CAR
Sally: Yeah, its not that big a deal.
Sally: Why are you yelling about it?
Tom: oops sorry Cap-Tourettes
Tom: my bad
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