Personally, I have a hard time with the slime factors of okra and Malabar spinach — they're downright muciliginous if not handled properly. Growing up, I couldn't choke down lima beans, and I just haven't attempted them again lately.
Other vegetables are simply challenging, even though I like them. Butternut squash, for instance, takes a sharp knife and some arm strength to deal with, and I just don't always have the energy.
What about you? Which vegetables challenge you as a cook, and why?
(Images: Nealey Dozier; Kathryn Hill)