Michael looking in a mirror, and having way too much fun with the color change option.
Michael You look a little pale there, pal. Let me fix that. [changes his skin color to yellow] You're all yellow from the scurvy. Arr, captain. [changes his skin color to green] Grr... Don't get the Hulk angry. Raaaahrrr! [changes his skin color to purple] Oh, there's Barney. "I love you, you love me, that jogger has giant boobies!"
At first Michael's reading off Morty's letter is very heartwarming... then Morty had to go and totally ruin the mood.
Michael: Like I Said, "Good Guys Need A Break". I know you'll do the right thing this time. Love Morty. P.S. Your Wife's Rockin' Body Still Drives Me Crazy.
It comes in the middle of one of the movie's saddest scenes, but Michael flipping Ben off as he lays dying in the street. Ben's face is what sells it...which is then followed by Michael motioning that he was just kidding and wordlessly tells him that they're cool.
Michael's reaction when he first witnesses the remote's fast forward feature on his dog. The dog zooms around the yard, does his businesses then goes back in his house to hump his toy duck. When Michael pushes play, the dog collapses in exhaustion. Michael rushes up the stairs screaming this line before it cuts to the next scene.