This mentor helps the hero very, very grudgingly (most likely because he/she was bored and/or had nothing better to do). Never gives encouragement or compliments, except maybe right before the hero’s final test/battle, and even then it might be a longshot.There’s a fair to good chance that said mentor either is a Knight in Sour Armor or Retired Badass.

Source: Cynical Mentor – TV Tropes