when one squeezes their ass cheeks together.
person 1: why does your ass look so toned?
person 2: im clenching my cheeks together.
Clenching involves you and at least 2 of your closest friends whom you have absolutely no sexual feelings towards. All three participants leave their clothes ON and squish into a twin size bed in a spooning position. Then proceed to bounce up and down/hump to the tune of "shots" by Lmfao while chanting "clench clench clench". Continue til exhaustion, then fall asleep maintaining position. Usually done when completely wasted. Often accompanied by feelings of "WTF" the next day upon reaching sobriety.
guy: did you get any last night?
guy 2: yeah, dude, I clenched these two hot roommates last night. They had ass for dayzzz.
guy: damn. sounds wild
Clench Means Fit or Sexy, Possibly Perfect in Every way.
Boy 1: Whoa! That girl was Clench.
Boy 2: Na, Sophie is Clench, She is just Perfect!
adj. - When you have little time to do something; close; difficult.
Not to be confused with what you do to with your ass cheeks to prevent poop from involuntarily exiting.
"We have to be there in 5 minutes, it's gonna be pretty clench."
"I have all day surfing lessons for the next few weeks; my schedule is pretty clench right now."
"The exam had so much on it I barely finished. It was pretty clench."
<person1 and person2 punch fists together>