Why do people get dumber when they are standing in line?

Here's an example.

I was at Subway today taking advantage of the $5 deal. Apparently so were about 50-other people. The line was long, it was at least a 15 minute wait to get to where you order.

There were two guys standing in front of me in this line, one was wearing business casual, the other was in a three piece suit.

They were having some sort of conversation I didn't pay much attention to. Not that I'm above eavesdropping, I'm not, but it seemed pretty boring.

So we're standing in line -- for at least 15 Minutes -- no bullshit.

When the 2 guys get up to the front here's how the conversation goes with the guy in the suit.

Subway Slob: What can I get you?

Business Man: Uh.... (long pause) Um.

[Everyone starts looking at this guy including his friend, we've been in line for 15 minutes. Now he can't figure out what he wants to eat?]

Business Man: (to himself) What kind of sandwiches you got here? (More Pause)

[Tension is starting to build, people at the end of the line are moaning under their breath. Literally like a minute has passed.]

Business Man: I guess I'll have a ham.

[Phew, relief]

Subway Slob: On what kind of bread?

Business Man: Um?

[Fuck]