It's a slippery slope.
Even with that disclaimer in your FAQ, things could get ugly for you.
IIRC, the "awesome" guy said that around 7% of the people they call get upset with hearing they're awesome.
I imagine your numbers, from recipients who don't get the joke or are caught in a bad mood, would be higher.
FWIW, I would never offer a service like this, not only b/c of the potential liability issues, but also for all the bad karma you could stir up.