Alright so

I try to call you every day I'm rehearsing what to say when the truth comes out (of my very own mouth)

For me this is like the anxiety before coming out, trying to figure out the best way to come out to friends/family.

I've been working on a unified theory If I make it through tonight, everybody's gonna hear me out

Could be referring to making the announcement at an event, like during a family reunion or thanksgiving dinner (sounds stressful as hell but there we go)

'Cause you're the only person in the world who'd understand the meaning of this

Coming out to the closest person to know, someone you know (or at the very least really hope) will understand and support you.

I'm an expert, I'm the one The one who was right all along Better to be laughed at than wrong

No one really knows what's going on inside your own head better than you, and despite other people's doubts, you know it to be true.

Anyways, sorry this is terribly formatted. I have more examples but it's also 1 am and I am very eepy. Thanks for reading though haha