They're not like that all the time. On store openings and launch days half of them have been up all night, they've been working towards it for weeks, and the blow off steam with all of that. That is by far the most ridiculous store opening I've ever seen though, usually there's clapping and wooing and high fiving but that took the biscuit.
A lot of Apple's staff, especially on store openings, are SO excited to be working for Apple they could **** themselves, and it manifests itself in such embarassing antics :/