IIRC, tsundere and yandere are puns- kind of.
Tsundere is a way to characterize an anime character (most often female) where they are at first are very cold and curt. Over time they warm up and become much softer and loving characters. Alternatively, they come off as harsh and curt but are very sweet overall. There's two types of tsundere- one is more cold than warm, the other more warm than cold. An example of a more cold than warm would be Inuyasha and of the latter would be Keiko (Yu-Yu Hakusho).
The pun comes from "tsun tsun" which describes the personality of a person as being cold/harsh/curt/etc. "Dere dere" describes the personality of a person that is loving/warm/fawning/etc.
Yandere is the same basic idea (as far as the pun goes). The "dere" comes from the same place as "tsundere." The yan part means that someone is obsessive/possessive/crazy. So, if someone were to be considered a yandere (again, usually female anime characters although it is not exclusive of males) they would love and be crazy about another character but be... crazy in general as well. See- Misa (death note), half the characters of Ranma 1/2, Naraku to name 3 easily recognizable ones.
I need more hobbies <_<