What bothers me the most is the egregious data types for any argument.
If it's a string, do this. If it's a list, do that. If it's a dictionary of lists, do this other thing.
No, I want you to force me to provide my data in the right way and raise a noisy exception if I don't.
Series and DataFrame have "alternate constructors" for this purpose, and the loc/iloc accessors give you a bit more control.
I agree that the magic type auto-detection is a bit too magical and sloppy, but you have to realize that data analysts and scientists have historically been incredibly sloppy programmers who wanted as much magic as possible. It's only in recent years that researchers have begun to value some amount of discipline in their research code.
No, I want you to force me to provide my data in the right way and raise a noisy exception if I don't.