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Having a nightmare but in the day, so it's just a mare since it's in the day.

Basically, another way of saying you're having a living nightmare, ie you're in a really shitty situation.
Today's been AWFUL. I thought my English Literature exam was in the afternoon, but it was actually in the morning. I missed the exam, and now I've been told I've been held back. It's like all my exam-anxiety nightmares came true! I'm truly having a mare!
by Lefty Power 123 September 06, 2018
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3
Messing up your hair, sometimes until it's big and fluffy Generally more for guys than girls
*runs hands through hair rapidly*
"I'm having a mare!"
by Fifihasherlife December 10, 2007
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