Okay, so I have access to someone who knows NOTHING about games. NOTHING.
Showed her a Mario cap, she did not know what it was.
So, let's expolit this all we can.
I showed her this: and asked her what she thought the game was about:
After about 7-8 seconds, she said, "Well... it looks like... is that the back of a car? -- is it a car driving game?"
So, drop your cover suggestions here and I'll report back.
Recently Spotted:
Foolz (9m)
It would be hilarious if she starts to describe every cover as, "A porn game with..."
"A porn game with a fish with a big mouth?"
"A porn game with a boy with a big stick?"
Video games are borderline porn anyway, so she'd be right.
Well if she's going to think all games are porn, you might as well show her this:
I just watched a gameplay video of Portal Runner.
Why didn't I buy a PS2 back in the day? This is why. 
I still in tend to play it one day.
It was a blockbuster exclusive IIRC (available for purchase only at BB).
And one more for the "gaming as porn" arguement:
I was at a Fry's Electronics where there were Playboy models signing this game.
I did not do it.
I regret it more than anythng more I have ever done in my life. Including the time I bought Argyle pantyhose and wore it under my clothes for 4 months.
Okay, now you guys are perverting the original goal. Stop jerking off and post some traditional game covers.