An ass that is so flat and unremarkable that it appears as though a person's legs are hooked directly to their back, and there is no ass in between. People with ass leg syndrome frequently wear pants that jack way up their crack, usually causing shit stains in their undergarments. People who are afflicted with this particular abnormality do not ever get laid because candidates for sexual activity have significant difficulty in finding the ass legged person's crotch, which is of course a prerequisite for sex.
Dude1: Damn, I'm really drunk and I need to get laid. I'd fuck that chick over there, but she's got an ass leg.
Dude2: Yeah, well you're mom's got an ass leg too, but that didn't stop your dad. How did he ever find youre mom's pussy anyway? Her ass leg would've thrown me off while hunting for her snatch.