In one Simpsons episode, Apu tells Marge to avoid the line with the old guy ("Grampa" Abraham Simpson) and that the fastest line is the one of the single guys.

Apu is giving Marge contradictory advice.

The old guy ("Grampa" Abraham Simpson) is in fact also a single guy.

Apu may have specified younger single depressed guys. I couldn't find the video clip anywhere still available to get the actual quote, so I'm going from memory.

The age of the cashier can be just as important, since they're usually doing most of the work.