He looks at his sandwich before he says it; he's showing that you don't even need accurate information to get people to do what you need.

sound potentially important, hurried.. and desperate for a favour- and people will try to help

That's the joke. Dade was utilizing social engineering to obtain information from a security guard.

Realistic or not, it's a great example of how technology is never stronger than its weakest link, and often that link is human.

He also called himself Eddie Vedder. That was part of the fun!