When he uses this word (think: "I left the bar at six" vs. "I went home at six"), there's some kind of drama involved. Maybe he got stuck in traffic or is hiding something he did that he shouldn't have.
The big thing to look out for is when he says "never" when "no" will do. It's a sign he's overcompensating. For example, if you ask, "Did you just look at that girl's butt?" and he says, "Never!"
Like never, it depends on how he uses it. If he puts "that" in front of a noun, like "that woman" or "that money," it's a subconscious attempt for him to distance himself from the word. This is a common trick of manipulators.
If he skips "no" and goes straight to "I would never do something like that!" when talking about a past event, be wary. For example, "Are you still talking to your ex?" "I would never do that to you!" "Would never" suggests that he plans to do it in the future.
If your guy is a Southern gentleman, then this doesn't apply. But if he suddenly says "ma'am" to you out of nowhere, be cautious. It's a sign that he's feeling stressed and knows he's in trouble.
"By the way…"
Liars use phrases like this to try to minimize what they say next—but usually it's what's most important to the story. Pay extra attention to what he says afterward.
Liars usually try to downplay what they say with this word, so pay attention when he says something like, "I know this is going to sound strange, but…" or "I know you think I'm lying, but…"
"Why would I do that?"
It's a favorite stalling line of liars, so they can buy a little time to work out what to say next. These phrases also fit the bill: "What kind of person do you think I am?” "Are you calling me a liar?” and "I knew this was going to happen to me!"