What do you call someone who starts arguments for their own satisfaction? [duplicate]

Solution 1:

I'll tell you what I use.

See firebrand defined by Merriam Webster as

one that creates unrest or strife (as in aggressively promoting a cause)

There are also simple words such as agitator, trouble maker, rabble-rouser.

Solution 2:

It may not quite be the word you are looking for, but pretty close...

Pugnacious.

It means inclined to quarrel or fight readily; quarrelsome.

Solution 3:

A contrarian is someone who takes an opposing view, especially for the sake of being difficult, contentious or in opposition to the generally held view.

Solution 4:

A provocateur is:

a person who provokes trouble, causes dissension, or the like; agitator.

according to dictionary.com.

There is a lively discussion of the etymology at Did Emma Goldman first use the term “provocateur”?.