Solange Knowles -- It's Hard to Fight Jay Z in That Dress (PHOTO)

It would be tough to punch and kick your brother-in-law when you're wearing ... whatever the hell Solange Knowles wore Monday night to the Met Gala.

Hard to believe -- but it's been a year since Beyonce's sister famously went ballistic and attacked Jay Z in an elevator ... during an after party for last year's gala.

Meanwhile, Bey stole the whole damn night when she showed up in a ridiculous sheer nude-colored dress.

Damned if she was gonna let Solange steal the headlines this year.