Tone Setter

Someone who escalates a situation; an instigator. “Setting the tone” is the phrase to describe said instigating. The tone setter could have absolutely nothing to do with said situation, but inserts himself regardless for entertainment and/or other nefarious motivations.

*Person 1 and 2 are having a civil discussion

Person 3: oh shit you letting him bitch you like that?

That nigga is a tone setter