From https://www.grunge.com/1662137/snl-cast-members-couldnt-stand-co-stars/
During his tenure with "Saturday Night Live," Tracy Morgan also took issue with some chronic behavior from fellow cast member JImmy Fallon.
In an interview with Penthouse, Morgan admitted that he really disliked Fallon's habit of cracking up during sketches, getting laughs by breaking character. According to Morgan, he wasn't thrilled with Fallon's "laughing and all that dumb [bleep] he used to do — he wouldn't mess with me because I didn't [bleep]ing play that s***," Morgan said, as reported by Page Six. "That's taking all the attention off of everybody else and putting it on you, like, 'Oh, look at me, I'm the cute one.'" Morgan, in fact, gave Fallon a stern warning — that he apparently heeded. "I told him not to do that s*** in my sketches, so he never did," Morgan added.
Morgan got revenge with the help of fellow "SNL" alum Tina Fey when they appeared together in the NBC sitcom "30 Rock." In an episode, Morgan's character, Tracy Jordan, mimics Fallon's sketch-derailing breakdowns when his character begins doing the same thing, purposely creating live-TV mishaps in order to get cheap laughs in the show-within-the-show's sketches
I haven't watched SNL in forever, but I never cared for Fallon when he was doing the skits. Couldn't put my finger on why at the time but that compilation pretty much sums it up. I thought he did okay with Weekend Update but Fey probably did a lot of heavy lifting there.