Nearly the worst nightmare imaginable is you standing in front of the crowd of strangers without any idea of what to tell them. You look ridiculous and people start laughing and pointing at you. And, on the top of it all, you are naked. This nightmare is quite similar to a real situation when you are being introduced to new team and have to produce good impression on all its members. Or, at least, any impression at all.
I was always scared of the first day in any new place. Nobody knows you, and all observe you curiously to define the species you belong to. Besides, you are surrounded with a whirlwind of new names and faces which confuse you but which you are bound to memorize immediately.