Do British people understand American slangs?

Nobody in the US says "trick out my ride yall!!!" You'd get your ass laughed at if you said something like that.

Note to foreigners: nobody speaks with all those stupid slangs and phrases you hear on TV. It's the complete invention of writing staffs. At one point, yeah, people said it, but by the time it shows up on TV nobody talks like that unless they're trying to be tongue in cheek.

So to sum it up, by the time you guys know of any slangs, not only do people no longer use them, but if they do they're making fun of something for being outdated and lame.

I would have to really agree with such, honestly. And even for the forms that are actually used in parts of the US, such as "dude" and like, these are very commonly actually highly regional in nature. One must remember that California and New York City are only small parts of the US, and yet in much of the media content that the rest of the world sees these are the primary parts of the US which are visible (even if things are supposedly set elsewhere). For instance, here in the Upper Midwest, AAVE aside, the slang used is often quite different from that one would be exposed to in much media content; honestly, what I hear being used in many TV shows quite foreign to me here.