Badboy
From Crusaderkings
"Badboy" is a measurement of a country's status among nations. Basically it's how much of a warmonger you've been. Aggressive nations will have high badboys while peaceful nations will have very low badboys.
While the game never lists the exact numerical score of your badboy (unless you search through your saved game file) it will list an approximation of it.
BADBOY IN-GAME DESCRIPTIONS
0 BB = We have an honourable reputation
1-2 BB = We have a respectable reputation
3-5 BB = We have a slightly tarnished reputation
6-10 BB = We have a tarnished reputation
11-15 BB = We have a rather bad reputation
16-20 BB = We have a very bad reputation
21-25 BB = We have an extremly bad reputation
26-30 BB = We are dishonourable scum
30+ BB = We are worse than Dishonourable scum
Badboy ratings above 10 often result in negative events (like vassals leaving your kingdom) so it's recommended to keep it below that level. Talented rulers must often balance badboy increases and reductions so that they can continue to expand without getting too high of a badboy score.