1 definition by MrMazMan

When someone you know, knows someone else you know, but they don't know that you know each other until you mention the mutual friends name 'Sean Mulligan' - to which the reply is usually "Oh yeah, I know him. He knows everyone!"
A: So how did you meet Andrew?

B: Through a work colleague, thanks to the Sean Mulligan effect.
by MrMazMan February 4, 2020
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