InSecurity here with a rant, kind of and advice for anybody facing the dreaded call to the bosses office. This subject which I now rant on came up recently, not for me, but for another coworker who is no longer with us.
Now a certain Carolinian Thrognar worshipper and I dwell on the 3 Ds: document, document, document. This is good advice, but there is both a corollary and a further concept: don't lie to the boss. Make your 3 Ds truthful and all your defenses when the boss brings you into the back office truthful. Lying will get you every time.
If the boss asks if you did a specific something wrong, such as were you playing computer games on the work machine, having friends visit during work hours, visiting dog fighting sites on the work machine, or god forbid, did you throw a monitor off the roof of the building... You need to answer truthfully because they wouldn't ask if they didn't have proof. Most of the small stuff is a slap on the wrist, but they will fire you for lying. I have had this confirmed to me by more than one manager and a person who is their shop steward where they work.
I know management has a horrid track record of lying to us poor slaves, but they sure can't take getting lied to.
Stay safe and truthful out there!