I think, because of the situation in particular, cross-faction Spy/Spy would be VERY interesting. I can see the fight in my head; another Spy would definitely go for the watch, shattering it on purpose to uneven the odds a little and take away one of his opponent's abilities. The electrical outlet might have been an accident; things escalating to outright brawling after the insult of breaking the watch. It also seems very Spy-ish to me for him to call his opposite all kinds of nasty names like "misbegotten low-born scoundrel" and things like that, especially if the low-born part is true... Who would know that better than another Frenchman? But the real reason I think it'd be interesting is the whole "this coulda been me" factor that you'd get with Spy/Spy. If things had happened the other way around... Or the "it could still be me" factor. If this Spy decided to get revenge, he'd know exactly what to do to inflict the same (in theory) problem on the other Spy. Then there's the whole empathy factor... Another Spy would understand things about not being able to TURN OFF the invisibility that someone else like a Scout or Demoman would not. My .02 :)