Fan Nickname: "Relativity" for the Ryouko/Asami pairing, due to their respective powers.
"TacClarisse" or "T-Clarisse" for Ryouko's TacComp, to differentiate her from Clarisse Von Rossum. (from whom TacClarisse took her name)
From Word of God, we have RBBG for "Ryouko Being Bad at Girlfriending" in reference to her incredible density when it comes to romantic matters, even those concerning herself, even one month after starting a relationship with Asami!
"Berserk Ryouko" for her state of homicidal rage occasionally showing up in dire battles, such as when she beat up an armored alien sniper, that just killed her teammate, to death, with her bare hands!
After learning that she wrote a book of lesbian "tips" in the past that she's eager to share with any fellow Magical Girl, Kyouko earned the title of "Lesbian Love Guru" among the forums.