A phrase to describe what happens when you are standing and waiting for something, and then a bunch of people come and form a line next to you. Hence causing you to have to go to the back of it.

To be in the know about something, to know more about a subject than most.

What happens when you get in what you think is the shortest line at the grocery store, but it turns out to take the longest, usually because the person ahead of you needs a price check, or wants to chat to the cashier.