I actually like that, I think that's what I'll go with! Short and simple - I don't know why I didn't think of it!
And I know what you mean, it's hard to tell how characters get along until they really get going! I can kind of see Del getting on Marcus's nerves, maybe just how irreverent and careless he can seem, but I could also maybe see Marcus making Del calm down a little bit, either way seems plausible!