I'm getting more and more to the point where if someone is a cis man and his Mastodon profile is just a long list of FOSS they use, I'm blocking them, because they generally turn out to be nobheads in the end - easier to just give them the boot now rather than in a few weeks
Other warning signs: running their own instance rather than being on an actual instance with other humans; lack of CW use (and getting mardy if you point it out); being someone who replies and argues with you if you post anything faintly techie related
FOSS people make me want to do well at university so I can get a good job and buy a Mac and not be a FOSS person any more