I would like to preface this with saying that this is my first full campaign of DnD and I’ve only done a single one shot before this.
So my party is made up of inhumans, including a large Fighter in all plate armor that we at the time didn’t actually know the race of, as well as myself, a Tiefling Rogue. We had been on a mission to escort a set of NPCs to a village, and one particular NPC was going to stay while the other left to go back now that his sister had made it here safely. Just as we seem to be in the clear, Aleksandar, our fighter, turns to the NPC and tries to persuade him that he should come with us since he is an adept fighter (he had killed a wolf in a fight earlier by hacking at it with a sword until it died but had had a bit of a breakdown in the process). I immediately asked if I could roll to backhand the very large, plate-armored man beside me, who acts as one of our tanks, as I am mute and cannot verbally express my disagreement.
I rolled a 19. Which wouldn’t have been a problem, since his AC is 20, so we thought it was fine until our other tank, a Tortle, points out that that is only Aleksander’s AC when wielding his shield. The shield that he had put on his back for easy carrying at the end of the last session which we had all forgotten, except for, apparently, Cabot. So now his AC was only 18. I hit for 1 damage, which wasn’t that bad per se, but when Cabot had whacked him earlier and missed there was no damage, so I was feeling a bit guilty.
Then Aleksander got in between a couple of NPCs to protect a girl and got backhanded across the face for 10 damage, starting a fight that almost got us all killed and/or arrested.
Needless to say that the next time that I went to whack someone I emphasized that it was a light bop up the back of the head, not anything worse. Didn’t even have to roll.