Thank you for tagging, apologies for not seeing this earlier!
I have two interview nightmares, both in non-legal jobs though:
1. Marketing Director - I tend to forget things a lot and the company I was interviewing with is a brand that owns a brand i.e. Company A is a brand in itself and owns Brand A which is another business service but marketed as if it was a separate company.
I forgot the difference between the two in the presentation round (third stage out of four), blanked out and then said "I think Brand A does this and Brand B does this".
Safe to say I didn't get the offer lol...
2. Marketing Executive - Because I hadn't been interviewed in a while I kept using lots of informal language during my practice interviews. I thought I resolved it but in my most recent role interview for a wealth management company, I said the words: "legit", "totally", "cool", "I know that's right".
I got the offer so I'm not sure what happened there... lol