I Accidentally Took A Colleague's Coffee To The Bathroom With Me

So last night at work, I was on the graveyard shift and had to clock in for another six hours before I could leave. We were super busy all day, and around 3 AM, my co-worker Mark brought out a fresh pot of coffee that he brewed just for us because we're the only ones up until morning. He asked if anyone wanted some since we both seemed tired. Of course, I said yes, how can you resist fresh coffee when it's the middle of the night and you've been on your feet all day? Plus, Mark is always so nice and thoughtful with those small gestures. Afterwards, my bladder was screaming at me to go, but I was so wrapped up in catching up on a report that I didn't want to break concentration just yet. So I grabbed a travel mug from the kitchenette and poured some of the coffee into it without thinking, Mark had already gulped down his share and left for his shift. But then came the moment when my bladder wouldn't wait another second, and before I knew it, I was walking off to the bathroom with Mark's freshly brewed, untouched coffee in my hand instead of mine. You can imagine my shock and horror as the realization hit me. 'Oh no,' I thought to myself, 'What have I done?' It was like a punch in the gut! But there was nothing for it now, I couldn't just leave the coffee on the floor or anything like that. So what did I do? I had to come clean and tell Mark about my little slip-up before he noticed his missing coffee, but it felt so humiliating. And when I returned with an empty mug, explaining how sorry I was over a fresh cup for both of us, he just gave me a funny look, chuckled, and said something like 'Next time, make sure you get your own.' I laughed too after that, because it's not the end of the world. But still, I couldn't shake the feeling of being an idiot. What do you think? Was I out of line to take his coffee? Or is this just one of those little blunders everyone makes sometimes?