This thread started out with the question of how to understand the
"triboelectric series".
Philosophical point: It is good to train students to answer the question
that _should_ have been asked, not just the question that was actually
asked. This is a crucial skill in the real world, all-too-often
undervalued in the classroom.
In this case, a good move might be to morph the topic toward "work
function." Note that that altavista reports 5165 references to that,
versus 93 references to "triboelectric series".