First things first: it was a terrible joke. Unacceptably mean, ludicrously dated (GI Jane came out in 1997) and just not funny. But that doesn’t matter. There is never any excuse for violence. The end.
Will Smith thought he was defending his wife, but she didn’t look like she needed defending. She’s not a helpless damsel, she’s a strong, independent woman, successful in her own right. Her response to the gag – a withering eye roll – was perfect, all that was needed. She had already handled it herself.
Her husband resorting to physical assault was the lowest of the low. That the ugly moment was broadcast all over the world also means the dangerous message that if a man loves you, he is violent around you has been reaffirmed to women everywhere.