Flaws.

"The right flaws will make your character more accessible to your audience and bring him to life, but the wrong flaws will make your audience despise him no matter what heroic acts he accomplishes. There are good flaws, and there are bad flaws."

These are from TvTropes. 

• Alcoholism (except when it leads to violence)
• Drug addiction (except when it leads to violence)
• Tobacco use (cigars, cigarettes, and especially pipes)
• Sexual promiscuity or (as long as it doesn't involve children, animals or the unwilling, like rape, zoophilia or necrophilia) 
• Reverse snobbery
• Being too cool to socialize.
• Being a klutz.
• "Sticking to your guns" even when the odds seem stacked against you (Which some may argue isn't even a flaw at all, except when it results in Good Is Dumb)
• Stupidity (as long as it stems from genuine ignorance, and not apathy or bigotry)
• Misanthropy
• Emotional aloofness, especially with Male Love Interests
• Lack of self-confidence
• Holding ridiculously high standards, especially with snarky comments.
• Being a Noble, Innocent or Tragic Bigot (Assuming they're a good guy of course), especially for people who grew up a long time ago or those with Police or Military backgrounds.
• A hot temper (except when it leads to violence)
• Laziness
• Cussing (except in the presence of the clergy, monarchs, aristocrats, the elderly, children, and sometimes women)
• Self-Deprecation
• Cowardice (except when failure to act causes someone else's harm)
• Weirdness and a lack of social norms, particularly in female love interests
• Clumsiness, notable in that it's often the single flaw given in an otherwise perfect character