There is no infamy/bad boy mechanic as such. Other than angering the people you attack, conquest does not make you appear to be a threat. Obviously, the leadership of a clan you attack will not like you that much if they survive the current war.
On the other hand, thanks to the plot mechanic, you can usually count on someone always plotting against you (or your clan) at any time, making declarations of war tricky. The time to unleash a plot against another clan, or against the leader of your own clan is, in my mind, the moment they move against someone else. That means that larger clans are naturally in a position to be more careful when DOWing others. If you have a weak ruler that is not well liked, attacking another clan might just encourage some of your more restive vassals to plot.
Bear in mind that honor not only is spent attacking other clans and plotting, but it is a factor in lord/vassal relationships. Generally, the higher your honor, the more your vassals like you. That means that weak rulers will be more inclined to hoard their honor to stave off unhappiness among vassals. Spending honor to plot or declare war might use up honor you need to maintain the goodwill of your vassals. It's not an infamy or bad boy mechanic as such, but it does provide a more complicated war/no war decision tree for players. You are not budgeting infamy or bad boy so much as you are budgeting honor within the boundaries of your ruler's ability to interact with vassals.
The AI seems to take honor and cash seriously; however, because there are more limits on internal development of your clan's kori (provinces), there is a point where it makes more sense to DOW someone else than it does to sit on your hands and promote internal economic development. The AI realizes this and, at any time, there are probably 25 or more small wars being fought throughout Japan, many of which are 4-way fights. The AI sends ninja to destroy province improvements more than it tries to assassinate people right now (or maybe the AI prefers destroying my province improvements based on an algorithm that sees how developed my provinces are). I also did not see any AI clans near me that spent their honor frivolously. (There may have been some that did so, but I suspect the AI may have forced those vassals and clan leaders to commit seppuku to solve that little "problem.")
There is no "concede defeat" function that causes a loss of honor; however, conceding defeat does cause the loser to give up a hostage, securing an enforced peace (the winner does not give up a hostage in this case
). This makes forcing other clans to concede defeat more worthwhile because they are unlikely to retaliate in the near future with the life of a hostage (and the penalty to honor) at stake.
