foible
A small, harmless weakness or odd habit in someone’s personality.
A foible is a minor weakness or quirk in someone's character, the kind of flaw that might be annoying or odd but isn't seriously harmful. Maybe your friend has a foible of always interrupting people when they get excited, or your teacher has a foible of making the same corny joke every single class.
The word suggests something we can tolerate and even find endearing, not a major character flaw. Your uncle's foible might be that he insists on telling long stories about “the old days” at every family dinner. Your sister's foible might be organizing her books by color instead of by title, which drives everyone else crazy but doesn't really hurt anyone.
Foibles are part of what makes people human and interesting. When we accept someone's foibles, we're saying “I see your quirks and imperfections, and I like you anyway.” Everyone has foibles: maybe you have a foible of tapping your pencil when you're thinking, or always wanting to be first in line, even when it doesn't matter.