n. a stupid oaf. (Also a rude term of address.) : I'm afraid I come on like a dumbbell sometimes.
Dictionary of American Slang and Colloquial Expressions by Richard A. Spears.Fourth Edition. Copyright 2007. Published by McGraw Hill.
Cite This Source
Word Origin & History
dumbbell
"weight used for exercise," 1711, originally an apparatus like that used to ring a church bell, but without the bell; used for exercise but sometimes also to practice ringing changes. Figurative sense of "blockhead" first recorded 1920, Amer.Eng.
[duhm-bel] 
