In the morning. When you sleep you're generally flatulent, sweaty, etc. So think about taking a shower and then marinating in that for several hours. No thank you.
Therefore, I take my showers in the morning before heading to work.
And for those who legitimately answered "... Bathe?" -- gross.
Is there a restriction that showers can only be done once a day? Cuz I do it thrice - in the morning before i head to work, in the afternoon after I get back home, and at night before i go to bed...