I'm happy to be here 

1. To have drunk 2 - 3 standard drinks; to be still completely functional; to be still capable of driving home.
2. To settle into the party atmosphere

Dude: Hey man, want a lift home?
Man: Are you sure? Your drinking tonight dude! *Points to beer*
Dude: Reeelaaax, I'm (just) happy to be here. I'll be fine by the end of the night.

I'm happy to be here by Blackstump November 13, 2003

I'm very happy to be here 

1. To have consumed 4 - 5 standard drinks; to be socially acceptably drunk
2. The only way to truly enjoy a party.

Dude: Hey man! Enjoying the party?
Man: *Slightly slurring* Oh I'm very happy to be here, thank you.

I'm very happy to be here by Blackstump November 13, 2003

I'm just happy to be here 

The kind of thing you say when you are put into an awkward scenario and you don't know how to react.
Real life example of mine below:

Girl: "So we want to get weed for 5 people tonight" (proceeds to look at me)

Me: I mean, I'm not really into that kind of thing. I'm just happy to be here.

I'm just happy to be here by EJS_Ethan May 12, 2022