However, the main reason is simply the fact that it's such a captivating example of unintentional humor, and what happens when you don't pay attention to your image. In many ways, it's the linguistic equivalent of the famous rabbit-duck optical illusion. It's curious and elicits a response when one realizes the double entendre.

It's hardly problematic, unless your definition of problematic is for everyone not to be dull as cardboard to every little example of unintentional humor in their lives.

A bit like PenIsland - or PenisLand. They get a lot of traffic from it.

I agree it is problematic if people are uncomfortable with the idea of gender reassignment and using that for humour. But then maybe that's a way those people use to get over those feelings of awkwardness and move to a place of acceptance?