I haven't seen any stereotypes for pansexuals, because I've hardly seen anything about pansexuals, or how they differ from bisexuality.
Pansexuals are simply able to be attracted to anyone, no matter their sex or gender. Bisexuality as a term just means that someone is attracted to more than one sex or gender, but not necessarily all. I called myself bisexual until I found out that the word pansexual exists, and what it means. So the stereotypes for pansexuals are basically the same as for bisexuals, but homophobes regard us as even worse, since we are able to be attracted to trans, non-binary, and pretty much everyone else they regard as "lesser" or "mentally ill."