"Petting the shark" refers to giving a woman a hand-job. This is due to the fact that at most aquarium shark petting tanks, they require you to pet a shark with the first and middle finger, the same two fingers used to finger your girlfriend.

Side Note: A woman's vagina also closely resembles that of a sharks brain, doubling the connotation.
Yeah, I'm totally about to pet the shark.
by smashuri November 2, 2010
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Performing an unnecessary overtly dangerous act.
The breaker panel was three feet away, but the electrician pet the shark and worked with the live wires.
by Mikey the Sub-Genius January 22, 2019
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