To have sex with an alien. In these terms clappingdoes not at all refer to slapping your hands together but instead the sound one makes while having sex.

This phrase became popular in 2019 when the Area 51 Raid was still popular. People used the term to mean that they would break into Area 51 and have sex with one or multiple aliens whilst there.
Person A: Imma go clap those alien cheeks during the Area 51 Raid
Person B: Rex that meme is dead get help
by Orge October 28, 2019
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Another word for literally demolishing and crushing somebody.
Peter: I need some support guys, it feels hard rn.
Ash: That’s what she said
*everybody laughs*
Peter: BITCH IMMA CLAP THOSE CHEEKS GET OVER HERE
by Membean Magician March 19, 2022
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