Noun, adj. Pretty damned stupid.
See also "tardostrong" and tardstrong".
After seeing your buddy break a tooth trying to open a bottle of beer instead of saying something like, "Now that is pretty damned stupid!" You could say, "Strongtard!" or "You're a strongtard!" or almost in a congratulatory tone, as if you were saying "Cheers" or "To your health!" you could say "Strongtard!"