I have edited this post multiple times, I'm trying to make this sound as clear as possible, hopefully it works.
It's very hard to explain to someone what taunt parties are, without the other person actually having participated in one. I can speak from experience, back in the Brawl era I would try to fight these Taunt Parties, and not understand why everyone was teaming against me, like they all had some sort of grudge against me.
Let me make something clear: Taunt Parties are NOT sitting there and taunting all day. That is a very boring room and I wouldn't blame anyone for leaving. They are instead a group of people that all commonly agree not to fight seriously, and instead mess around doing silly things. This could be anything from 4 jigglypuffs resting each other, you could even be practicing tech skill if you're that hardcore, just try not to hit anyone on purpose.
The sole purpose of Taunt Parties is that people want to have fun playing a game without fighting, either because they just want to mess around or they are bad at fighting and just want to make friends. If they team up against you, that's because you want to fight and they want you out of the room. Personally I do not like the 3v1's and I will sit off to the side, but that is honestly their way of forcefully removing you from the room in attempt to find someone that is friendly.
It's a sad concept really, beat them or join them, regardless they aren't just going to go away no matter what anyone does. I'm just trying to convince anyone that they are not as boring as they sound and you should at least give them a chance.