there's also a weird trend of mostly dudes doing that with really rapid speech patterns while expanding their mouths wide for consonants. it's something you won't necessarily hear unless you've had vocal training - it just sounds weird unless you have - but if you know what to listen for, you can't unhear it. the combination of all of these factors makes it really hard to understand people, akin to a thick accent, except that they're using standard US English. I've never needed captions to understand teenagers before - I've not always understood some new slang but this speaking/editing style combo is something else.