I’ve used the phrase “Me paenitet” a few times without knowing how it works. “Me” is the first person personal or reflexive pronoun in the accusative or ablative. “Paenitet” is second conjugation, PAI, third person singular. Literally it seems to be:
“It displeases/offends me,” or “it is causing me regret.” Me is a personal pronoun, accusative. Verus?
Whoa, you’ve thrown me a curve ball. If I Google “me paenitet” I’m sorry I receive a lot of relevant hits. However, if I Google “mei paenitet” I’m sorry or
“paenitet mei” I’m sorry I get nothing back.
Also, “memoria teneo” is ablative: to hold by means of the memory.
Are you sure about that genitive usage?
It is an idiom, aliquod memoria tenere, so acc. with that. However alicuius oblivisci (to forget something), memorare, meminisse etc. take the genitive.
Sorry, disregard what I said! paenitet does take a direct object, genitive of thing that causes the grief. My first truly grievous error in a long time, maybe someday I will recover. 
Did you know that Vergil was murdered by Octavian?
Yeeeees! I finally got one! 
Are you greening me?
lol Quis non?
Though I think it was Livia. 
CONSPIRATIOESTDICO