"Was he bluffing?"
A bluff was a deception tactic built on an empty boast. It was a common tactic in games like poker, but also had applications in real life. One such example of a bluff applied in real life was the Corbomite Maneuver. (TOS: "The Corbomite Maneuver")
H-bombs were built on 20th century Earth as a bluff, never intended to be really used. Upon encountering the Planet killer in 2267, James T. Kirk theorized that it served a similar goal. Upon being accused of bluffing, Spock later claimed that Vulcans never bluffed. (TOS: "The Doomsday Machine")
In 2268, while Kirk and a Klingon crew under the command of Kang were fighting under the influence of the Beta XII-A entity, Kirk threatened to kill Kang's wife. However, Kang called his bluff. (TOS: "Day of the Dove"
In 2269, while the IKS Klothos and the USS Enterprise were trapped in Elysia, the S-2 graf unit of the Klothos suffered damage, but it's captain, Kor, tried to bluff Kirk by pretending they were doing fine. (TAS: "The Time Trap")
When the USS Enterprise-D was being held hostage by Nagilum in 2365, Jean-Luc Picard responded by initiating the ship's auto-destruct. Nagilum ultimately responded by releasing the ship. (TNG: "Where Silence Has Lease")
During a discussion about Romulan strategy between Mot and Jean-Luc Picard later that year, Mot opined that there's a time when you want to call a Romulan's bluff and there's a time when you don't. Picard countered that one did not always have the luxury. (TNG: "Ensign Ro")
Benjamin Sisko, according to Jadzia Dax that year, was a terrible bluffer, at least in poker. She claimed that she had spent two lifetimes trying to improve his bluffing, but to no avail. (DS9: "Paradise")
In 2375, during the Dominion War, a conflict emerged between Bajor and the Romulan Star Empire concerning the arming of a Romulan hospital on Derna. Colonel Kira attempted a daring bluff, taking a fleet of Bajoran impulse ships to prevent an approaching group of warbirds from reaching the moon, even though they would not be a match for even one warbird. Kira hoped that the Romulans would not dare endanger their alliance with the Federation by firing on the ships. Ultimately it was not the Romulans, but Starfleet Admiral William Ross who blinked, with Ross threatening to remove the hospital using Federation forces. (DS9: "Shadows and Symbols")
Kathryn Janeway was also an occasional bluffer. In 2375, Janeway tried to bluff Y'Sek, a bounty hunter, but he called her bluff. Confronted with an Class J nebula lifeform in 2376, she successfully bluffed the creature by creating a situation where, if it did not cooperate, they both would die. (VOY: "Think Tank", "The Haunting of Deck Twelve")
In the Enterprise-D senior staff poker gameEdit
During a 2368 game, Riker and Beverly Crusher discussed bluffing as Crusher called Riker's bluff only for Riker to predict that Crusher was going to call his bluff again a little bit later, each basing their correct calling of the other one's bluff on "just a feeling". Crusher joked that when Riker bluffed, he raised his left eyebrow in a particular way. (TNG: "Cause and Effect")