Deadpool 2 has some great moments, but the absolute funniest might be the scene early in the film where Deadpool arrives at Xavier's School for Gifted Youngsters. It contains a fantastic cameo by the entire current cast of the mainline X-Men movies. It's one of the funniest cameos in the film, mostly because it's pretty surprising to see. It turns out the actors were pretty surprised to see it as well, as most of them thought the scene they were filming was meant for the end credits. According to Evan Peters who plays Quicksilver...
We did a bunch of different versions, some not PG, and they ended up using that one. I thought it was going to be for the end credits -- and I think everybody kinda did -- but it ended up being like, boom, right there sort of in the first half of the film. Which was really sort of weird and shocking.
The reason that Evan Peters, and apparently the rest of the actors didn't realize what they were filming is because, as we had learned previously, they weren't actually on the set with Ryan Reynolds at any point. The scene of the X-Men was shot on the set of X-Men: Dark Phoenix and then digitally inserted into Deadpool 2. The actors apparently didn't know what was happening outside their shot. Perhaps since they knew they weren't going to be a larger part of the movie, they thought the scene was meant as a post-credits scene where it would exist out of context just for the laugh. Peters tells ET Online there were multiple versions of the scene; hopefully, we'll see them in a future Blu-ray release.
In fact, the scene comes fairly early in Deadpool 2 after the Merc with a Mouth has attempted to blow himself to pieces. Colossus brings the pieces back to the X-Mansion to rehab and Deadpool, as he did in the previous film, makes jokes about how empty the school is. The camera then cuts to a new angle that shows all of the current X-Men, from Quicksilver to Beast and more, in a room behind Deadpool. They notice him, and they quietly shut the door before he notices they are there.
And it makes sense that a cameo like this could have been part of the post-credits scenes. It's a pretty big moment in the film and quite often laughs like that are left for the credits. Of Course, Deadpool 2 had other plans when it came to what it did during the credits.
While Deadpool will never be one of the X-Men, he started up his own X-team in Deadpool 2. This will lead to the X-Force movie that is set to take place down the line. A larger team movie means a bigger budget, which in turn could mean future cameos for the X-Men. Perhaps we'll see these two teams working together down the road.