“I swear, I'm the least funny person on the planet… mgaaaah!!”

Simplified Meaning:

The person is saying they believe they are not funny at all, and they are very frustrated by this. Imagine you're at a party where everyone is telling jokes and making each other laugh, but when you try to tell a joke, no one laughs. Instead of joining in on the fun, you feel awkward and start getting annoyed with yourself because you just can’t make people laugh like others can. The phrase "mgaaaah!!" at the end shows they are really upset about not being funny and maybe even a little bit embarrassed. To cope with this feeling, someone could focus on other strengths they have. Maybe they are good at listening and giving advice or have a special skill, like cooking or playing an instrument, that others can appreciate. It's important to remember that everyone has their own unique talents, and you don't need to be funny to be valued by others.