You are good at threatening people
Check: you can change another's behaviour with a successful check, or demoralise them in combat (as per the Intimidate skill description in the 3.5 PHD).
Action: Varies. Changing another's behaviour requires 1 minute of interaction. A rushed Intimidate check can be made as a full-round action, but the character takes a -10 penalty on the check. Demoralising an opponent in combat is a standard action.
Synergy: 5 or more ranks in Bluff gives you a +2 bonus to Intimidate checks. This bonus increases by +1 for every additional 10 ranks (that is, +3 at 15 ranks, +4 at 25 ranks, and so on).
Feat: the Improved Demoralise feat allows you to use this skill to demoralise opponents in combat more quickly.