My sister gets her nails professionally done with acrylics and that really hard stuff (shellac? Not sure) but filed really short. The nail techs always think it's weird. But it makes it basically impossible to chew her actual nails.

I like to think about all the things I touch - door handles, toilets, bus rails etc - and how all that nastiness gets under my nails and how gross that would be to put in my mouth.