Top Definition
The act of masturbating in one's sleep.
Teenager: Mom, can you wash my sheets? I had another wet dream.

Mom: God Dammit, have you been sleepwhacking AGAIN?
by the dirty liberal July 27, 2009
When a man is masturbating while asleep.
Example 1

Friends Wife - "Can I ask you a personal question regarding your friend?"
Husbands Friend - "Shoot!"
Friends Wife - "I caught my husband masturbating while he was asleep and I could not wake him up."
Husbands Friend - "Was he making Gorilla sounds?"
Friends Wife - "YES! YES HE WAS!
Husband friend - "What you witnessed was an art form known as SLEEP WHACKING, sleep whacking is multi-tasking at it's best."

Example 2
My buddy was telling me about his marital affair the other night. It involved him sleep whacking and it put him in the doghouse.
by deucebiggss1 February 28, 2014
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