At the height of Breaking Bad's popularity, in Episode 12 of its fifth and final season, "Rabid Dog," Babylon 5 is mentioned.
The mention occurs in a scene starting at 13:32, during a conversation between protagonist Walter "Walt" "Heisenberg" White, his lawyer Saul Goodman and Saul's associate Patrick Kuby, as they discuss the whereabouts of Jesse Pinkman:
WALTER: His buddies, Beaver and what's-his-name?
PATRICK: Uh, Badger and Skinny Pete. Yeah, I know, he's not with them.
WALTER: They could be covering for him.
PATRICK: I posed as a meter reader. I put a bug in the tall kid's mom's place. For three hours straight, all they talked about was something called Babylon 5.
Badger and Skinny Pete's interest in science fiction was previously established in Episode 9 of the fifth season, "Blood Money," during a scene in which Pete explains his theory on how transporters work and Badger proceeds to pitch, for the next 2 minutes, his idea for a Star Trek script in which Chekov has Scotty using the transporter to help him cheat during a pie-eating contest in order to win against Spock, but Uhura causes Scotty to make a fatal mistake. We can only imagine what they would have had to say about Babylon 5.
Breaking Bad star Bryan Cranston, who portrays Walter White, previously played the part of Ericsson, the Ranger Captain of White Star 14, in Babylon 5's fourth season episode "The Long Night."