Knaidlach,
1. What about someone who does not want to be called a Yid, either because he wants to leave knows that the word is often a pejorative, wants to Jargon to philologists or is a proud non-Ashkenazi?
2. See Pitchei Teshuva YD 116:10 that there is an opinion that someone who does not accept an observant Jew’s word that his food is kosher is a heretic as he opposes Chazal, who said that a single witness is believed regarding prohibitions. As for his kashrut not being up to “your standard”, what about one’s standard in ben adam l’chaveiro, avoiding mechzi k’yuheira, etc.?