A slang term referring to semen. "Man-spackle" is compared to a white spreadable wall plastering compound, hence, "man-spackle" tends to be a word used by common blue-collar workers in the construction trades.
Example 1: I pulled my penis from her vagina, and ejaculated a load of man-spackle onto her breasts.
Example 2: My girlfriend came home with dried man-spackle covering her tramp stamp. What a white-trash whore she turned out to be!