After a night of fighting thugs and punks, Pete's costume got all torn up. He came home quickly to see if Mary Jane was there, but she wasn't. He took one of her spandex shirts and tore it up to cover up some of his wounds. What kind of idiot tears up a super-models spandex shirt?!?! Anyhoo... he ends up fighting Typhoid Mary. The upside-down Spider was only in issue 213, so I think that it was an accident.