everyone throws around the words chillul hashem for anything embarrassing, but what does it actually mean in the sources?

1. the gemara in yoma 86a defines it by example: a person who learns torah but is not pleasant with people in his business dealings, people end up saying woe to him who learned torah. and the same daf gives the opposite: a person who learns torah and is pleasant and honest in his dealings, people say fortunate is his father who taught him torah, and that is making the name of heaven beloved, kiddush hashem. so is the main arena of chillul hashem and kiddush hashem ordinary daily behavior and business, not big headline scandals?

2. where is the actual line? does the torah scholar’s standard apply to every jew, or is regular bad behavior by a regular person a different category?

3. and on the severity: the same daf in yoma says that for chillul hashem, teshuvah does not have the power to suspend the punishment and yom kippur does not have the power to atone, rather all of these suspend and death finishes the atonement. does that mean there is no real teshuvah for chillul hashem at all, or that teshuvah works but in a harder and slower way? and what is a person who already did one actually supposed to do?

bottom line: what behavior today actually counts as chillul hashem, and is there a way back from it?