It's a non-optional social CONVENTION.
The Big Bang Theory Season 1, Episode 16
No, it's the accepted CONVENTION.
The Big Bang Theory Season 2, Episode 21
Did you tell them that
you're holding your CONVENTION
The Big Bang Theory Season 7, Episode 14
Let's see, the magic store,
the Doctor Who CONVENTION,
The Big Bang Theory Season 10, Episode 19
Try telling him
it's a non-optional social CONVENTION.
The Big Bang Theory Season 1, Episode 16