The official policy for this forum is that we endorse cruise line rules for personal beverages, which means we don't allow messages which promote bringing liquor aboard. As long as this thread doesn't go there, we'll leave it open.
Royal Caribbean's policy is the most strict. It can be viewed HERE
I've personally not heard of anyone being kicked off the ship for breaking the rules. I imagine it would depend on the severity of the attempt, the level of deception, the amount.
However I have personally known of guests who were summoned to the security area, where their luggage had been quarantined because they suspected it contained booze. They were required to open it, and security took the liquor, and I imagine a record of the attempt was logged. It was returned to them at the end of the cruise.
If luggage is unlocked they don't need you to be present. I don't know if RCI does it, but Carnival does. One of our suitcases was opened and searched by Carnival. It didn't have any prohibited items in it, but they thought it might. When we opened that bag there was a letter on top of the clothes saying they had searched it.
All luggage is x-rayed, using high end equipment as is used by TSA.
Personally, I think it should be this way: If a bottle of liquor in it's original container is identified, confiscate it. If someone is using a rumrunner, beer bra, or has poured booze into a mouthwash bottle, they can no longer claim ignorance of the rule. I'd be fine with their being denied boarding. A couple object lessons like that and word gets around.
Another thing to note: in many U.S. jurisdictions, carrying liquor around in public in a non-original container is a misdemeanor. Even having the seal broken on the original bottle can be against the law.
A rum and coke (or any similar mixed drink) goes for around $6. Close to $7 once the 15% automatic gratuity is added.