FRGS means "Fellow of the Royal Geographical Society".  In the UK, the Royal Geographical Society (RGS) is a very old and still revered society dedicated to the gathering and dissemination of geographical information and research.  There are two ways to be named a "Fellow".  1. You do some interesting exploring or writing or research in the area of Geography and an existing Fellow nominates you.  Plus you have to pay a few hundred quid a year.  If your nomination is successful, you can put FRGS after your name on correspondence.  For those who love capital letters after their name, it's cool.  And, it can lend a bit of gravitas to whoever you are and whatever you are doing.  This first way is how Ripley Davenport got to be an FRGS.  He was awarded Fellow status in mid-2011.  Given that time frame, the only geographical events Davenport could have been credited with were all the fake expeditions he has now confessed to AND his solo walk across Mongolia in 2010.  But there are substantial unanswered questions about that 2010 walk and in the absence of evidence that Davenport claims to have, one could conclude that he faked that walk as well.  The second way to become a Fellow is to be a regular, dues paying member (several hundred quid a year) for five years and then apply.  

So, clearly the best and most defensible way to have FRGS after your name is if you were nominated by an existing Fellow for actual accomplishments.  And if you were made a Fellow on the basis of lies and deception, what then?