Oh, i-it's just this
DUMB crystal wand
The Big Bang Theory Season 12, Episode 2
Although, on the other hand,
babies laugh a lot and they're DUMB.
The Big Bang Theory Season 10, Episode 9
Because you'’re being DUMB.
The Big Bang Theory Season 12, Episode 3
...looks DUMB, take your pick.
The Big Bang Theory Season 6, Episode 2
Which was DUMB.
The Big Bang Theory Season 10, Episode 22