When one does the clenching of the buttocks. In embarassment or fear.
Agatha's buttocks clenched.
by ButtockB February 26, 2017
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1 Noun. The clenching of the Gluteus Maximus.
2 Adj. A word used to describe a tense, awkward or painful moment. This word was used by Bear Grylls whilst making a dangerous descent down a rock cliff in Man Vs Wild.

Buttock-clenching is a phrase used by British people.
1 Buttock-clenching helps strengthen the Gluteus Maximus.
2 That fall looked buttock-clenchingly painful.
by JMUK July 14, 2012
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