Knight Time, an episode from Superman: TAS where Batman goes missing and Superman puts on his costume to help out in Gotham. So funny!
I'd give a link for the Justice League episode, "Hereafter", but the youtube link I had seems to be gone. *sadness* But in this episode, Superman dies in front of the whole Justice League and Batman gets a bit weird with his cape fragment souvenir, and his denial, and declarations in front of a big 'S' monument. *sniff*
Superman putting on the Bat costume is hysterical, yes, but the funniest thing is that he does a decent job with it. Of course his slip-ups, with Tim anxiously telling him what to do, are funny. What's the greatest part of it though is that he *can* do the role, what with the voice imitation and getting into the snarl and bitch-slapping of various Bat-villains. And for someone who claims that he and Batman aren't "exactly friends" in the beginning of the ep, this is something that he couldn't have accomplished without careful observation. He does such a good job that the villains don't even suspect that it's not really the Bat.
sidenote: How adorable is it when, at the end, Superman says while he turns away with a little cape flounce - yes, flounce! - "For a loner, you sure know how to pick a partner." And Tim's surprised *hearts* face of 'Sing my praises some more, O Superman.' We don't get to see it, but I'm sure Bruce put his head in his hands with an 'Oh no, not *again*!' Hee!
And in "Hereafter", Batman stands by his pile of death-junk collected from where Superman died, exclaiming, "He's not dead!". All while holding a piece of Superman's cape and *fondling* it. Yes, *fondling*, because he doesn't just hold it, he *strokes* it with his *thumb*. Strokes! He refuses to go to the funeral with another "He's not dead!" denial (although he does lurk on a rooftop to watch the funeral procession), but then he goes to the memorial monument, when he's sure no one else is around, and makes his declarations to "Clark". Not Superman, *Clark*. Gah!
But is he all smiley and joyful like the rest of the League (such as Diana who says, "I like the beard. Are you going to keep it?") when Superman finally returns all He-Mannish and stripped down and burly? No! He glowers some distance away with the I-Did-Not-*Miss*-You of "I knew you weren't dead." Hee! Oh Bruce, you are *so* messed up.
I am full of weird fannish glee.