You're not going to know, not at first. There's just not going to be an "a-ha!" moment. The thing about liars, is if they feel they got away with it once, they'll keep it up. And they'll get increasingly sloppy and risky with their lies. Eventually, they'll trip themselves up in front of you.

So if you want to know how to tell if a guy is lying, then just be patient.

I'll also add that there are great liars and lousy ones. The great ones, or even the very good ones, are the ones you have to give as much rope as possible too in the hopes they'll hang themselves sooner or later. The lousy liars usually have one major "tell," which is poker-speak for a quirk, tick, or action that betrays someone's poker face. A lousy liar always talks too much. They explain too much. Good lies, like truth, are short. Just the bare facts. Lousy liars think that overly complicated excuses, or answers are somehow more credible that brief. Oh, are they wrong.

Wait. Be patient. Good things come to those who simmer. Otherwise, if he came home late one night, stinking of booze and covered in glitter, and proceeds to tell you a story about helping out friends with broken hearts, or rescuing crippled kittens out of trees, or other noble, absurd late night charities, then he might be trying to blow smoke up your bottom chute.