If you really want to get technical, yes, bathroom breaks or any break for that matter is -EV, monetarily speaking. I know you were joking, but it's easy to figure out the loss without a calculator. If a bathroom break takes you 5 minutes, you lost 5 minutes of playing time, and you should know how much that is from your hourly EV.
I do think breaks are -EV. When I'm at the casino I wan to get as much action as possible. In fact, when me and supercool played in that 3-card poker promotion we were really extreme about breaks. It was so good we did not want to miss a single hand. We estimated our EV to be about 2.50 per hand, and I dont want to pay 2.50 or 5 bucks to go take a piss, lol. We played for about 12 hours straight, with hardly any breaks. I only took a break when they were changing cards, or making a complicated payout that took the dealers a while.
Anytime I have gone to the bathroom is has actually been +EV. I only go to the bathroom during a negative count. Sometimes I go when I dont even have to. When I do really have to go, well I hold it in until a negative count hits. If it takes a while, it sucks not going to the bathroom, but I should be getting paid for it with the nice counts!
So yeah, I'm extreme enough to even base when I take a break on EV. Those little 5 minute breaks add up after a while. Counts bad enough to wong out occur frequently enough that you should be able to time any breaks you need to a negative count. If you gotta go anyway, you might as well make it during a negative count and save yourself some money.