"Made up my mind to date both of them
by pretending to be TWIN brothers."
The Big Bang Theory Season 9, Episode 14
...since I beat out my TWIN sister
for the "Did It On The Potty" trophy.
The Big Bang Theory Season 8, Episode 23
She's my TWIN sister.
The Big Bang Theory Season 1, Episode 15
I have a TWIN sister
whose assaults began in utero.
The Big Bang Theory Season 3, Episode 17