Shake, Meatwad, and Carl trying to console one another after Frylock is diagnosed with cancer in "Party All the Time". Most of the episode is the typical Black Humor sure, but...geez, even Shake is worried about him. Shake, Carl, and Meatwad all treat things as though they aren't protected by series-induced immortality. And by this point in the franchise, Frylock has never died. Not once. He's effectively the only character whose death could actually be permanent. The second episode of Aqua Unit Patrol Squad changed that, but the point stands.
A big YMMV: in the movie Shake kills Meatwad out of pure craziness but his reaction a few seconds later is pretty much one of the few times, if the only time, we see him genuinely remorseful for his actions, showing some degree of concern for Meatwad.
It's actually very revealing: Shake believes that Meatwad is invincible, and therefore, he can harm him with impunity. When it appears otherwise, though...
All of "Party All The Time". Everyone's Played For Comedy attributes are employed...Shake is willing to destroy the sun if Frylock is cured. Meatwad's line "Well, you should tell them that you don't have cancer" is fucking brutal.
In A PE Christmas, Meatwad is given the chance to sing "Silent Night" for Shake's Christmas-themed rap album. It's actually done extremely sweetly, even if Master Shake's eel-induced diarrhea is loudly heard in the background. Better yet, Flavor Flav likes it! Bonus points go to Michael the sound board technician, who records Meatwad's song even though Master Shake ordered him not to.