I remember growing up and my mom always telling me to not take a shower while it was thunderstorming. I've done it a few times but I always try to keep the water not flowing over my body in case it ever did happen it wouldn't cross my heart and kill me.
So, can you be electrocuted while taking a shower during a thunderstorm?
Take a look at this document talking about lightning myths - http://newweb.wrh.noaa.gov/hnx/LightningMyths-1.pdf
You must avoid any conducting path leading outside, such as corded telephones, electrical appliances, wires, TV cables, plumbing (including plastic pipes with water in them), metal doors or window frames, etc.
Also from here: http://indianapublicmedia.org/amomentofscience/can-lightning-strike-you-in-the-shower/
Metal is a good conductor, so if lightning strikes an unprotected house, chances are the current will travel through any metal pipes. What’s more, the tap water moving in these pipes contains impurities that help the water conduct electrical current.
When you’re wet, the natural resistance of your body is cut by half, and the salt and contaminants on your skin decrease your resistance further. So basically, being wet can make the difference between an unpleasant electrical shock and a deadly one.
It happens.
I'm sure there are more examples than just this, but these two examples were on the first page of search results. You don't have to look far.
In 2007
http://www.thesun.co.uk/sol/homepage/news/article491125.ece
In 2008
http://www.kcci.com/r/16265120/detail.html