daf bit: Sanhedrin 27

The mishna is discussing who is ineligible to be a judge or a witness, enumerating close relatives (brother, uncle, father-in-law, brother-in-law, son-in-law, etc) [*]. R. Yose adds: anyone who inherits. R. Yehudah says the restriction applies even if you are no longer so related, if you once were. Further, the rabbis say, a friend or an enemy is ineligible. What is meant by a friend? One's groomsman. Enemy? Anyone who, by reason of enmity, has not spoken to one for three days. (27b)

The text later says that an enemy can sometimes be a witness but in no case can be a judge. I don't see a discussion of how "enmity" is evaluated. (What if you say I'm snubbing you and I say I'm just inattentive?)

[*] I am using shorthand here; the text says things like "your sister's husband", which is how R. Yehudah's case can come up (your sister died; is her husband still ineligible?).