Muddy Boots
What a gut-stick occasionally resembles after using the back door, due to the horrifying debris deposited upon it.  Boots worn in the pouring rain, such as those sported by John Terry when he's slicing penalties wide and bawling his eyes out, tend to become caked in mud.  So do men's members when they've been upto the apricots in shit.
Upon withdrawal his triumphant smirk faded in a heart-beat, realising as he did that his giggling stick was spattered with more filth than a pair of muddy boots.