Gal threatened to call my office and out me, but I ignored her and she went away.

 
Maybe just lucky, but I suspect most potential extortionists will never follow through.

 
For one things, you might remind them that the penalty for extortion, in most states, is 20 years.

Not sure if it was an attempt or was legit. Had a provider contact me stating that she was pregnant and that I was a candidate for responsibility due to timing and the 98% effectiveness of condoms. I let her know that I have been merrily shooting blanks since my vasectomy 18 years ago. Her reply - "okay". So I don't know if it was real, but I have avoided her since.

Yep ...

10 or so years ago, an escort was asking guys for 1k, 2k, spewing some BS story.  After falling for it, and never getting the promised "I'll pay you back" money and ignored, I made the mistake of warning guys (without divulging the ladies' name or info, just a generic "don't loan gals cash" message).  Other guys started joining in, mentioning her name as being taken for $ and asking if it was her who got me.  I never mentioned her name or said yes or no to them.  She blacklisted me and posted all my private information, threatened me, all kinds of stuff.  I had to have my attorney pal send a C&D to her address and she still complained to him for a few YEARS, saying I had ruined her income stream and life.  Was a crazy time, very stressful for a long time too. Man ... (sigh)....

But if you blow them off as "JUST AN EXTORTION". Then be extremely careful that she is not truly pregnant. Cause she could go through the legal system. Take her to a Clinic for blood work and ultrasound and get 2 copies (1 for her and 1 for yourself) this way she can't go back a few days later and say she is. That would be proof on that.