Caitlyn Jenner doesn't know jack about the trans community's most important issues, so she should just shut up ... so claims the woman who got all up in Caitlyn's face. 

Ashlee Marie Preston tells us she took Caitlyn to task because she needs a quick education about how her decisions affect the community. As we reported, Ashlee went after Jenner Saturday night at L.A.'s LGBT Center -- unleashing a rant about why she should stop supporting Trump.

For the record, Caitlyn's already sworn off the Prez. Still, Ashlee thinks she's tone-deaf, and needs to bone up on several issues if she wants to rep the community.

Ashlee Marie Preston