"Wretched reptiles" is probably the most iconic, or at least it's what sticks out in my mind as being memorable or in the vein of a catch-phrase.
There's probably one or two that I find very amusing, but I can't remember right now, it's all a blur.
More than the insults, I recall action dialogue. My all time favorite was a line of Rocksteady's, he brandishes a laser rifle & says "Drink blazing electric death!" as he fires it. So gnarly. & I always crack up during that scene where Splinter's nonsense ninja move is accompanied by the battle cry of "Sacagawea!".