[Jokes on you, Shouichi; Shizuo didn't even think or guess about which was true! This is nothing to be proud of. There's a bit of an incredulous look at Marx, given what he thought was funny. Him and the pale-haired kid were just plain suspicious. All he could respond to with Marx's question was muttering;]

How would that make us friends...

[While he doesn't mind a change in 'activities,' he didn't want the kid to make the choice again. Or even have his sarcastic suggestion be taken seriously.]

I'll pass if that's the case.

[Nope, pushing it back towards the other guy. Just... someone not the one he feels like he should want to punch.]

You got a better idea then?