It’s suggesting people really into films get annoyed that other people aren’t as into films as them to know about the niche films which they insist are the only good ones.

As the other comment says, it applies to any hobby - e.g:

It’s suggesting people really into paint get annoyed that other people aren’t as into paint as them to know about the niche paints which they insist are the only good ones.

It’s suggesting people really into pickle get annoyed that other people aren’t as into pickle as them to know about the niche pickles which they insist are the only good ones.