When a girl takes your dick out of your pants and not all of it is out of your pants/boxers and the girl thinks that's it meanwhile, it's only the tip or half of it.
Emily- Oh my god I jacked this guy off the other day and his dick was so small I didn't even let him take his pants all the way off because I wasn't interested.
Sebrina- Are you sure it just wasn't the tip of the Iceberg?
Emily- What?
Sebrina- since you didn't let him take his pants off all the way maybe they hid half his dick so you couldn't see it...therefore it being the tip of the Iceberg