Trigglypuff was the name the Internet assigned to someone as a meme and as an insult.
There was a speech to be given by several far right-leaning people at the University of Massachusetts - Amhurst in April of 2016. A large group of self-professed social justice warriors (SJW's) showed up to disrupt the event. For future context, this was during the run-up to the 2016 presidential election and the American public, particular the younger demographic, was in turmoil.
As the speakers, Milo Yiannopoulos and Christina Hoff Sommers, took the stage for their lecture, the leftist folks in the audience started handing out pamphlets and shouting down the speakers. One of them stood out for her words and how she acted.
Cora Segal, who also goes by other names, was quite animated in her protest. Because she happened to be obese (yet still comfortable in her own skin, as she stated later), images and videos of her yelling and flailing around in anger hit the Internet. The Internet being what it is assigned her the moniker "Trigglypuff", a portmanteau of "Triggered" and "Jigglypuff", a round Pokémon creature from the animated video and gaming world.
Unfortunately, the term still comes up whenever someone wishes to insult anyone who is obese and actively protesting in an animated fashion. It's a surface insult, ignoring the subject of the protest to belittle a physical charactistic of the protestor.