It's not a pickup line but it can be an icebreaker...
When the conversation is going on about sharks, shark diving, etc... and the girl freaks out and says something like "ooh, I love diving, but sharks just scare me to death, I think I would freak out if I saw a shark"...
You very seriously reply that in your extensive diving experience, you have learned a way to make a shark instantly go away.
She will say, "Really? What is it? Please tell me in case I ever see one of those ferocious creatures!!"
You then say if a shark is coming at you and you want to make him go away, you just to do this... and put your hand over your eyes.
It is cheesy, but it might get you a laugh and maybe a punch on the arm.