How about the Carolina Reaper:
He looks thrown together from scraps from other robots
When he is out gassing it sounds like flatulence
When it ignites you hear a some weird robot laugh
The robots it summons stumble as if drunk
add other funny bits within game mechanics
American Machines, that sounds funny and terrifying at the same time 
Haha, wow. Yeah that would be a funny boss… 
What kind of loot would it drop?
Like a ton of Carolina Reapers lol, and it could drop a schematic where you use the peppers to make incendiary rounds XD
That is amazing, if done correctly that would actually be pretty cool.