I think the word you're
looking for is... "INVISIBLE."
The Big Bang Theory Season 5, Episode 17
Sheldon, I've spent
most of my life feeling INVISIBLE,
The Big Bang Theory Season 9, Episode 17
Invisible, unwanted and unloved...
The Big Bang Theory Season 4, Episode 22
He's just friends with
an INVISIBLE trumpet player?
The Big Bang Theory Season 11, Episode 17
...this is for the INVISIBLE kids.
The Big Bang Theory Season 8, Episode 22