Usually when something terrible happens. This varies from but is not limited to: an old grandma/grandpa wearing a thong at the beach or remaining stuck in a parallel parking spot because the two douches left you no room to leave.
A lengthy contraction. Use it your own way, who knows what it actually means. It’s too rusty to translate. The word can be found on Reddit, Tumblr, and probably more, most likely originating on social media.
Mike: who'd'ven't'f'I'dn't've'nt'f'I'd'ven't'f'Ihavn'tn't'd'I've-
John: Mike, shut up, we’re in an interview