The Manhattan Back Smack is when your conducting anal sex with a gagged hog tied lady while under the effect of at LEAST 10 Viagra pills, you then smack her in the back of the head with your penis until she becomes disoriented OR passes out.
You finally finish the job by unloading a sea of hot sticky man milk on to her face...Then run like hell
Jerome: Bro! Where did you disappear last night?
You: Hey you know that hot piece of ass from last Friday?
Jerome: yeah what about her?
You: Well guess who gave that bitch the Manhattan Back Smack!
A condition caused by excessive lint (commonly present in a new pair of underwear) clinging to the scrotum after the first use. The fuzzwill fuse with ball sweat or Fermunda Cheese giving the appearance of an African-American's scrotum.
Trisha was disgusted at my Black Sack! She didn't believe that it was from my new pair of Fruit-of-the-Loom boxer briefs.