In the eighth season episode "Business Guy", Peter Griffin forces his father-in-law, Carter Pewterschmidt, to invite his office workers to a Big Bang Theory viewing party. Later, he is seen watching and enjoying the show by himself. Jim Parsons and Johnny Galecki provide the voices of Sheldon and Leonard:
Sheldon: I'll have you know I can bench press over 690 billion nanograms.
Leonard: Sheldon, that's less than two pounds.
Sheldon: It sounded better the way I said it.
Penny also appears, but as she has no lines,
The Big Bang Theory is also referenced twice in the show's ninth season. In "Welcome Back, Carter", Peter blackmails Carter with details of his affair, and to keep him quiet, Carter gives him his oversize flat screen HDTV:
Peter: I keep not laughing at The Big Bang Theory, and I figure it's gotta be the television. You know? TV this size? Forget it, it'll get me laughing until I got snots falling out of my nose.
Additionally, a later ninth season episode was entitled "The Big Bang Theory", which references both the show and the actual theory of the universe's birth.
In the episode "Our Idiot Brian", Brian says Sheldon's former catchphrase: Bazinga. Peter then makes a reference to Sheldon's actor, Jim Parsons ("the gay scientist").
Two And A Half Men
In the tenth season in an episode entitled "Bazinga! That's From A TV Show", Jake uses this line and refers to the frequently used catchphrase.