yup words can't be taken back. but the actions the person takes after saying certain words matter and can make the words a vague memory of the past.
if their actions after the harsh words are spiteful and more harmful that confirms their true nature: they were always a viper waiting to strike and won't stop striking until blood is drawn.
if their actions are sincere and determined to amend and correct what was said or done, that shows they're human and do make mistakes. but the rite of passage for everyone involves a mistake and the steps taken after the mistake. for some this can be life altering.
but

don't let it get you down. if your heart was in the wrong place when it happened, as in intentional and callous, then you wouldn't be worried about it now. and be lucky you're one of the few with a conscious,
UNLIKE the person who took the printer knowing they didn't pay for it. the good part is God does not grant blessings to those who have something obtained in an offensive way (ok I could insert an invading Iraq reference here

, but read Joshua Chapt 7. I ain't no high holy humble servant of God, but from what I understand you can't expect peace and blessings while holding on to something that wasn't obtained rightfully or honestly, as in that item you obtained via deceit is more valuable than God because you're holding on to it tighter than the word of God, which clearly states the right thing to do. so better to have a clear conscious now than pay for it later yanno)
I'm the type to return something. I even returned something to the delivery guy because I didn't order it, it was an extra soda. only to find out he charged me for 2 after I had a chance to check bill! but my first instinct was this isn't mine, maybe it's for another delivery and what if he has to drive all the way back just to get a replacement soda. I kid you not, all that went through my mind in a matter of 30 secs. but I was later credited for their mistake.
but have a sincere talk with your manager, if you have a decent relationship with him/her. also some things happen for a reason for you to see people's true colors and to remind you to keep on your toes. and do you really want to work for a company which judges you entirely on one thing that's happened in retail all over the world! or someone who understands you do matter?