Any time you have a title that garners some degree of respect in society, you're going to get some fakes who want the respect without putting in the work. Forget about the law ... just don't tolerate it.
My advice is to out the guy (or gal). Tell them point blank that you, quite frankly, think they are full of BS. Ask them some pointed knowledge questions or ask for some proof. I would never fault someone for challenging me on this.
I think you'll find that they gladdly offer some proof or offer some weak defense and then quietly go away and look for easier targets. Either way, problem solved. And by being authentic about your suspicions, and kindly confronting your faker, you'll garner some trust from your peers in the process.
The Navy SEALs deal with this stuff all the time:
http://information.usnavyseals.com/us-navy-seals-info/10-ways-to-spot-fake-us-navy-seal/
Be well,