Show-er

"Growers" are guys whose penises tend to contract a lot lengthwise when flaccid, while "show-ers" are guys whose penises could be said to merely "deflate" without contracting much in length.

One kind expands and lengthens when becoming erect (a grower). The other appears big most of the time, but doesn't get much bigger after achieving erection (a show-er).

"I'm a grower. You're a show-er," Robin says, looking downward, comparing himself to George with a self-conscious pang.