Bastian burst out laughing when she started singing. He tried to interrupt her, but he was just laughing too damn hard, so he wasn't able to actually spit anything out until she'd faltered and said that they weren't going to work out if he couldn't sing.
"I'm terribly sorry to tell you, but I'm not going to wake you up early anyway -- much less singing that song!" He paused, then added in a joking tone, "Now, maybe showtunes..."
Which was actually kind of possible, with Bastian, being the theatre and music freak that he was.
But when she said Spiderman.
Oh, they were going to have to have a little chat about that, because seriously now. Spiderman?! His tone turned completely serious as he looked at her with an expression that expressed his utter shock and horror at what she'd said.
"Spiderman?! You're kidding, right? Batman is like... twenty million times better than Spiderman. Hell, the only superhero worse than Spiderman is Superman." In other words, no, he didn't have Spiderman sheets.