What happens if i get caught using an ID that isnt mine trying to get into a club in las vegas?

Its not "If" but "When" Vegas is tops in the country for catching fake/improper I.D.'s. No bar/club/casino is going to risk losing their liquor/gambling license over something like this. Its not like elsewhere in the country where they confiscate the ID and throw you out - they prosecute to the fullest extent of the law. And using someone else's ID is even more stupid - identity theft is a federal offense.....

Security keeps the ID and can the cops and have you arrested/detained

Using the I.D of another person, especially in Las Vegas, is an extremely STUPID thing to do. It constitutes identity theft even if the other person gives you permission to use their I.D. It would be better to be caught with a fake I.D in your own name. Contrary to that "What happens in Vegas" slogan, Nevada is a very conservative state, and does NOT tolerate crap that some states, like California, let you get away with. When (not "if') caught you WILL be arrested, you WILL be prosecuted, and you may spend several years in a Nevada State Prison with cell mates eager to teach you the "ins & outs" of prison life.