Do you remeber in Friends SO01E13，about“sparky”
Do you remeber in Friends SO01E13

Roger: You're so funny! He's really funny! I wouldn't wanna be there when- when the laughter stops.

Chandler : Whoah whoah, back up there, Sparky. What'd you mean by that?
what‘s the meaning of the sparky ？

Question

Do you remeber in Friends SO01E13，about“sparky”
Do you remeber in Friends SO01E13

Roger: You're so funny! He's really funny! I wouldn't wanna be there when- when the laughter stops.

Chandler : Whoah whoah, back up there, Sparky. What'd you mean by that? 
what‘s the meaning of the sparky ？

Answer

Something happened earlier that Roger is hiding.  Chandler realized soothing is net being said.  Sparky is a term for someone excited.  This is how puppies end up with the name.  Chandler is saying, Ok, you are excited... Calm down so you can tell me what you are hiding.

Answer

I'm not sure, I can't recall seeing this episode but if Roger had his hair up in a spiky way or if he behaves somehow like a pet then maybe that's why he's called Sparky.
But I would have to see the episode to be sure.
Hope maybe this helped :)