I feel like a lot of folks who are only familiar with Phineas and Ferb via the memes get the impression that one of the show's central gags is about the titular characters gaslighting their sister, but that's not what's happening at all. They're generally 100% open about what they're doing, and lots of people know about it. Even their dad is frequently in the loop. It's the mom in particular who absolutely refuses to believe that anything unusual is going on, and while part of that is due to the evidence having a tendency to vanish right before she walks into the room, there's also a lot of refusal to entertain the possibility involved – heck, there are multiple episodes where the boys admit what they're doing to her face, and she just dismisses it as them doing a bit.
Basically, what's being sent up in the show is not "brothers gaslighting their sister", but "eldest daughter whose mother never believes her about anything, even when disbelief requires wilful blindness to what's happening right in front of her face". Which is still kind of a fucked up thing to be playing for laughs, of course, but you can see where some folks would find her worryingly relatable!