Grannie, mommies, aaaaaaaaand,,,,,,,,,,,, trannies.
Timber seems rather obsessed with gender bending, and if you notice, with certain sprightly personalities at least, it's, well, downright flirtatious.
It wasn't REALLY insulting you at first, it was tugging you ponytail. If you had nipped back with a sharp but playful tongue, it'd be outright flirting with you.
Unfortunately, like many, you bit back the wrong way. Dimby saw a sensivitive spot it can attack, and that gives it a hardon as well, albeit one that requires no part from you other than taking its bait.