> The average level of American "OMG so excited to meet you" is usually reserved for actual celebrities in Europe

I've been an American all my life, and I've never seen anyone say they were excited to meet someone other than either an actual celebrity or someone who has been significantly talked up in advance to the level of being at a quasi-celebrity level in context (and even in the latter case, “I'm glad to finally meet you”, possibly followed by an explanation of the reason they've been looking forward to it, is much more common than expressions of excitement.)

Honestly, the behavior you seem to be describing is one which would strike most Americans as both unusual and deeply disingenuous.

Things are very different from one part of USA to another, and even from one social group to another. Though I haven't participated in any social situation where "OMG so excited..." is the norm, it is easy to imaging it exists.

my experience (as us-born/bred) is that this exists, but is more a personality trait than anything else. And some personality traits can co-exist among others with the same trait more easily, and that 'so excited' outward expression can often get amplified in a group, but even individuals can be like that. I don't see it as uniquely American, but... it may be somewhat here. By comparison, traveling in Russia, public displays of enthusiasm/positivity/emotion were far less common at all (although in small groups of friends they came out).