Gary's evil twin in "Mine's a Double" singing "Anarchy in the UK" at the Royal Oak.
When he travels back to Victorian London, Gary is mistaken for Jack the Ripper, and is chased by an angry mob. He manages to duck into an alleyway, and the mob goes in the other direction. He breathes a sigh of relief...then the camera pans out to reveal that Jack's standing right next to him.
Gary's lament in one episode.
Gary: You know, I read somewhere Stephen Hawking is close to unraveling the mysteries of the universe. Good, maybe he can give me an answer for why Time Travel gives me gas?
In the first episode of Season 2, Gary decides to attempt a Compound Interest Time Travel Gambit, and goes to a local bank to deposit a large amount of money. He meets the bank manager and his employees, who behave (and are named) exactly like characters from Dad's Army. Then 'Mainwaring' asks if he can help Gary, prompting him to start singing "Who do you think you are kidding Mr. Hitler!"