Back when I was a kid, on some mornings, I did try sitting down to urinate a few times (basically whenever I was feeling too tired to stand), but I stopped doing that after a while since it would usually hurt (I’m guessing due to the force of all the urine coming out (quite a bit does accumulate after sleeping for 8 – 10 hours) combined with my sitting posture). Since it never hurt while I was standing, I ended up just sticking to that after a while.