The act of sexual intercourse in the urethra of a member of the female. Pleasure is greatly increased when the penis enters the bladder. Be warned that urethral sex, or U-SeX as it is called on the seat, may result in unwanted urethral pregnancy and permenant physical damage.
My girlfreind really loves me, so she allowed me to have some urethral sex with her. I made the mistake of not using a condom, and we ended up with an unwanted urethral baby. It's life is nothing but pain, as it's veins flow with urine. Poor child. Urethral sex: be careful.