Commander William T. Riker: In your position it's important to ask yourself one question: what would Picard do?
Wesley Crusher: He'd listen to everyone's opinion and then make his own decision.
The Outcast - S5-E17
Deanna Troi: All right. This hand, the game is "Federation Day."
Worf: What is that?
Troi: Well, the Federation was founded in 2161. So...twos, sixes, and aces are wild.
Worf: That is a woman's game.
Troi: Oh? Why's that?
Worf: All those wild cards. They support a weak hand. A man's game has no wild cards.
Beverly Crusher: Let me get this straight. You're saying it's a woman's game because women are weak and need more help?
Worf: Yes.
Encounter at Farpoint (1) - S1-E1
McCoy: How old do you think I am anyway?
Data: 137 years, Admiral, according to Starfleet records.
McCoy: Explain how you remember that so exactly.
Data: I remember every fact I'm exposed to.
McCoy [looking at Data's ears.]: I don't see no points on your ears, boy, but you sound like a Vulcan.
Data: No, sir. I'm an android.
McCoy: Hmm...almost as bad.
The Pegasus - S7-E12
Admiral Blackwell: [seeing the banner] Captain Picard Day?
Captain Picard: Oh, uh... Yes, it's, uh...it's for the children. I'm a...I'm a role model.
Admiral Blackwell: I'm sure you are. Starfleet out.
Guinan: I hear they drummed you out of the Continuum.
Q: I like to think of it as a significant career change.
Guinan: Just 'one of the boys', eh?
Q: One of the boys with an I.Q. of two thousand and five.
Data: The Captain, and many of the crew, are not yet convinced he is truly human.
Guinan: Really? [Picks up a fork and stabs Q's hand.]
Q: AAARGH!
Guinan: Seems human enough to me.
Capt. Picard: Tea, Earl Grey, hot.
Capt. Picard: Engage!
Lt. Cmdr. Data: If the warp drive fails to activate, the results could be... Unfortunate.
Lieutenant Worf: Very unfortunate. We will be dead.
Capt. Picard: Make it so.
Answer: Yes. The doors to the holodecks can be locked when in use by anyone aboard the Enterprise so they couldn't be disturbed. However, high ranking officers like Captain Picard could override the doors as it's seen that overrides are in use even for the crews quarters. Even Barclay, when he's indulging in one of his fantasies could have the doors to the holodeck unlocked by an override code.