From another board about muscle cars
"ONE more time.....a 'MUSCLE' car was a MID-SIZED, BIG-BLOCK POWERED, AFFORDABLE 5 OR 6 SEAT car starting with the GTO option on a LeMans in 1964 and continuing until the last BIG-BLOCK, MID-SIZED, HIGH-PERFORMANCE car was offered for sale to the public."
It refers to a class of car.
The newer Mustangs are ugly as hell -- ever since the Mustang II and Fox bodies they've been ugly as hell to me. No, I take that back -- in 1969 they went ugly to me