My really obvious one, and a huge source of problems for me, is Discord. But the biggest one was a wild one:
Irfanview
It is a super-fast image viewer and simple image editor. Supports every format I’ve ever thrown at it. Bulk conversion and resize works like a charm. Hell, it’s half the reason I haven’t moved to Linux for my daily use.
I fairly regularly work with someone who, in their organization’s alias scheme, was given the email address of an 80s cartoon villain. It rules so much and I doubt she’s even in on the joke.