Stargate SG-1 S10E8 “Memento Mori”
This is a joke about how there are a lot of actors who portray characters in both Stargate SG-1 and the X-Files (just like basically every other sci-fi show filmed in Canada). Carter, Hammond, Dr. Lee, etc. I found out recently that IMDb has a neat advanced search function that allows you to compare two shows to quickly see which actors appear in both: https://www.imdb.com/search/name/?roles=tt0106179%2Ctt0118480
The actual dialog in that scene:
Sal, what am I doing? Working here, sleeping out the back, watching reruns of the X-Files in my spare time. I appreciate everything you’ve done for me, but… I’ve gotta tell you, I’ve been thinking about leaving.
Bonus: A remastered version of an old meme that is another Vala meta crossover
Stargate SG-1 S9E5 “The Powers that Be”
There must be a scene where Mulder tracks down Cameron Mitchell after he gets shot down but before he joins the Stargate program. Mitchell, wheelchair bound due to his injury, drinking heavily, and on Morphin, confesses the whole truth to Mulder. " I was shot down in Antarctica while defending earth from an alien invasion by a fleet of ships. I was leading a squadron flying a secret fighter jet built with reverse engineered tech from crashed alien spacecraft. We only won because a general in the USAF got control of an abandoned weapons platform built by other extinct aliens."
Cut to Mulder and Scully leaving the apartment building “And you think I’m crazy. This guy fell down the weekly world news rabbit hole and hit his head on every rock on the way down.” Mulder says.
“I didn’t see any of those magazines in his apartment Mulder. He’s a decorated colonel in the air force.”
“The best of us know to hide the stacks of UFO magazines when we have company.” Mulder quips.
My only issue with this is that Mitchell would NEVER disclose these secrets even to an FBI agent.