I haven't heard of such thing (urinary retention) until last year, when a friend had the same problem.

On the contrary, a few years ago I suffered from frequent urination, went to see a doctor (I was convinced it is a STI, but doctor said it's a mental problem, and he was right and I got over it by training my bladder).

In gay porn, there are few videos where people push something down their urethra, or pull something out. I had an urethral swab years ago, an unpleasant experience.