Satanists don’t worship the devil. They are typically hedonists who, very much like @King_Pariah said, believe that Satan simply represents the opposite of Christianity. Relishing in this life, taking joy in all of the “good” things life has to offer… rather than abstaining from many that Christianity tends to preach against.
No, I wouldn’t keep my distance simply because someone considers themselves to be a Satanist. It’s just a belief system, and it is no more disturbing to me than any other. I do know Satanists, and they get up and go to work and have kids and are “normal” people in every way imaginable. The religion that speaks to them just so happens to have a scary name.
Of course they “act normal” in public. Most of them probably act normal in private, as well. This glorified, Hollywood version of devil worshipers sacrificing babies is pretty much nonsense. Satanists do not worship the devil, they worship themselves, and this is very clearly stated in the Satanic Bible.