Well… uh…
It's not uncommon for a cartoon show to scratch the surface of bad taste from time to time. It'll probably happen again for the sake of a cheap laugh.
My thoughts? April Derp would have best been suited as a scrapped idea. It was obviously going to ruffle a few feathers. Not everything has to be tip-toed around, but come on, it wasn't even that funny. Also, if I may be sensitive for a moment, Casey calling Irma 'nasty' was baffling. It's humorous to mistake Splinter for Irma, but why add on 'so nasty'. Is it because her style illustrates typical adolescent angst? Is it because she's a little overweight? I don't see anything repugnant about Irma.