beat the meat
Masturbate, as in He was always beating the meat. This term, considered vulgar slang, is used for males, since it uses meat in the sense of “penis,” a usage dating from the late 1500s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.