To be caught up in the awkward situation of insulting somebody's mother, the mistake being that she's (supposedly) deceased.

Those seconds that follow the person's remark of their mother being dead are what define the word.

Act commonly consists of the person retracting their statement as a precautionary measure.
1: "My mum used to buy me Pop-Tarts
2: "Your mum is a Pop-Tart"
1: "My mum's dead."
2: "Oh. Mumistake. I didn't mean to... you sure she's dead?"
1: "No! Dick!"

1: "My mum used to buy me Pop-Tarts"
2: "Your mum is a Pop-Tart"
1: "My mum's dead."
2: "Oh. Mumistake. I didn't mean to... you sure she's dead?"
1: "Yes. I'm going home to cry myself to sleep."
by Redlineonhill February 12, 2008
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