The classic fabric fail spot
Yellow, I haven't had any bike shorts "fail" in that spot, but oh, I have a zillion pairs of jeans that have rubbed through and ripped in the upper thigh area. The latest pair? Just today.
Driving home from an evening of eating and drinking and soaking at Chico Hot Springs, Montana, through Yellowstone National Park, we came upon a traffic "bear jam." So we parked a quarter mile away and walked back to find a distant view (150 yards?) of a black bear mother and her cubs. Being short, I had to hop up on some fallen tree trunks to see over the crowd. Riip, the left leg upper thigh area gave.
Of course, these are my favorite 2-year-old Lucky jeans, and I patched the right thigh about four months ago. Time to quit with the wine, dessert and baked goods!
Your saddle might be the culprit
Rubbing on your saddle bag (or the velcro that wraps around the seatpost) is an obvious cause of the dreaded inner thigh hole. Usually, you notice scratches or pilling on the fabric before they rub all the way through. Or, you'll feel the shorts rub/pull on the velcro.
However, I've also found that the repetitive motion of my shorts rubbing on my saddle rails will do the same thing. My saddle is very narrow and the rails are actually just a bit wider than the nose. In this case, I can't feel the rails rubbing on my shorts, but they do.
I've also known folks who've gotten the hole from the nose of their saddle.
So many holes, so little time.....