Brazil's humiliating 7-1 loss to Germany wasn't just bad ... it might be the most EMBARRASSING thing that's ever happened to a World Cup team ... so says Piers Morgan.
The former CNN host -- and die-hard soccer fan -- was out at Madeo last night when he WENT OFF on Brazil ...
"The most incredible thing I've ever watched in my entire 49 years of watching football," Morgan said ... "It was like an abattoir. A footballing abattoir."
For the record, "abattoir" is a fancy French word for "slaughterhouse."
Morgan's trashing of Brazil continues -- and he explains why the ass-kicking was actually GREAT for U.S. soccer. Check out the clip.