This is a sound effect for some things like a comic relief, or if it’s a sound that comes from having sex. Often a joke to make your friends chuckle till they have a asthma attack.
Example 1:

John: *makes a meaty whack on his thigh*
John and Steven: *both chuckle*

Example 2:

Bruce :I’m gonna roll in this locker room with my big dick! *sets his dick on a table to prove his dominance, henceforth causing a meaty whack*
by Mikeyisameme June 25, 2018
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