What if someone's name is actually Demo?

Well, then I suppose we will be adding another unfortunate event to his/her life... and with Demo as a name, even FlowMingle couldn't help much ;)

According to a quick search, "69 People found that match Demo in the state of California." I noticed 1 or 2 with the name "Demos", but other than that.....

Perhaps, since sign-up as "Demo" is special functionality anyways, you could ask the user to confirm that they're "Demoing" the account or if their name actually IS "Demo".

Albeit, 69/36.5m < 0.0002% of the population so you could probably get away with letting the user know that they're been automatically "Demo'd" and only fix it if you have to.