the obvious answer is,
they engaged in COITUS.
The Big Bang Theory Season 5, Episode 1
Oh, okay. As long as it doesn't end
with us having COITUS with him, I'm in.
The Big Bang Theory Season 9, Episode 13
She has COITUS one time,
suddenly she's Gloria Steinem.
The Big Bang Theory Season 10, Episode 5
Technically,
that would be COITUS interruptus.
The Big Bang Theory Season 1, Episode 1
they just stay home
and have constant COITUS.
The Big Bang Theory Season 11, Episode 9