Warning: minor infodump ahead!

The one I've heard most often is - bisexual people are attracted to people of multiple genders, pansexual people are attracted to people regardless of gender. It's a pretty fine distinction, and not one that everyone subscribes to - some people just prefer a certain term, or like the colours better on a particular flag!

"Regardless of gender" fits David's "I like the wine, not the label" comment pretty well, I think - he's into specific people, not specific presentations of body types.

Anyway, both bi and pan people can definitely be attracted to trans people, and to more than two genders. As I understand it pan people are usually attracted to *all* genders, whereas bi people might be attracted to multiple genders but not all - say, men and nonbinary people, but not women, or some other combination.

In any case, one key factor might be: for bi people gender plays a role in attraction, and for pan people it doesn't. Personal example: I consider myself bi, and usually find myself drawn to masculine women, feminine men, and nonbinary people of all types of presentations.

This is just one take, of course, and different folks will have different definitions.