Anyone else have characters they can't write?

I am writing the first few chapters of my Sunset Shimmer story and I am realizing that I CANNOT write Pinkie Pie at all! She is so hard to write for me, as is SciTwi.

For Pinkie I can't get her enthusiasm and randomness down and SciTwi is too smart for me to write easily (I have to constantly do research just for her dialogue) so i've been trying to limit how much dialogue I give them.

Does anyone else have characters they just suck at writing?