- Your character gets defensive, edgy, paranoid. Maybe for good reason.
- Do you believe in justice? If so, who is not getting their fair share of bad karma? Even the scales by doing something unfortunate to the character that has suffered the least.
- Which character, if killed, would really mess up this whole situation? I know, they are too important to kill off. But due to pressing family problems, they could leave indefinitely.
- One of your antagonists is or becomes very wealthy. How will they use this against you?
- Peer pressure [or hazing] is fun, especially when it convinces your character to shoplift, tresspass or go naked.
- An assumed name, identity, role: someone is not who they are pretending to be.
- Tomorrow morning your character rolls over and sees the fruit of last night's mistake on their pillow...more interesting: maybe they don't regret it. [The original said "sleeping on their pillow" but leaving it out opens up the possibilities! :-D]
These are from Random Plot Points where there lots of random ways to muck up your plot. :-)