A person with seemingly limitless energy, often known to randomly turn up outrageously drunk and dance around on their own making as much noise as physicallypossible.
Tsun (ツン)= standoffish, mean, rude
Dere(デレ): fawning, lovestruck, caring
And so, if we put them backwards, we get a person who is loving and flirty at first but then becomes mean, rude and cold later.
Person one= Did you here? That girl is a deretsun
Person two= really? Who would've known. I just thought she was a deredere