Basically, you have normal thighs, then they get fat (tier 1). But when they get likeeven fatter, you get another level of fat like a hill of fat(tier 2), which is loose off the other fat so when a thunder thigh is being walked besides the legs (tier 1) rubbing against eachother they (tier 2) hit eachother making a noise, hence thunder coming into the expression, most likely to because of alliteration for a dramatic, comedic affect. This sound can have a brighter tone and richer feel if accentuated with bumpy cellulite
Damn, those thunder thigs are so massive it looks like shes got a second arse
It's like someones stuck balloons in those thunder tighs
No, no....come on, this cant be real, that girls got thunder thighs ripping out like the hulk
when a chick's booty is so fat her thighs look like canons of muscle that could choke a horse. men are initially attracted because of the hourglass effect but once she gets naked you realize you're really just having sex with an enormous woman.
chick thinks she's hot but truth is no one wants those 50 pound thunder thighs. god damn woman put down the chicken wings and eat a salad.