What does it mean when a guy says "I'm a grower not a shower"?

I mean, im assuming he's taking about his thing but what's the point and what is he really saying?
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We were at a party and this guy, a friend of my boyfriend was interested in this girl there and she said lets all go skinny dipping in the pool/hot tub so he said, "I'm a grower not a shower" and everyone laughed. But I wasn't sure.
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+1 y
Are most guys growers or showrers?
What does it mean when a guy says "I'm a grower not a shower"?
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