An extremely overweight individual who cannot walk without their thighs making a thundering clap.
This term has been used mistakenly to myself.
I had a horrible bicycle accident when I was young and my right thigh was ripped open, even though they stitched it with 16 stitches, I still feel pain more than 10 years later.
This part they stitched isn't flat like the rest of my thigh so it tends to rub against my other thigh and because this accident made it hard for me to be active, yes I am a big guy - not a fat guy, my legs are more muscle than fat, I can bike my 280 body up a vertical hill on a 1 speed freestyler (sometimes I can't do it though..my right leg goes completly numb) well thats why I am not offended, because I am not the one your joke is even ment to be aimed at.
"John had a terrible accident, and now years later some few jealous - ex girlfriend co-workers are calling him 'thunder thighs', which is mistakenly used and is way out of context.. John thinks they should go F$!$#@ themselves!"