The Office Prank Gone Wrong...

I started working at this new company a few months back. It's been fine, but I've felt the need to connect with my coworkers more. So I thought, what better way than pulling a little prank on someone? This guy, let’s call him Alex, he always comes in super early and starts drinking coffee like there's no tomorrow... which sometimes there isn't for him because of how late he stays at night too. So yesterday morning, before anyone else got here, I filled his mug with hot water instead of coffee. It was just a harmless joke to get us all laughing. But when Alex came in and poured what he thought was milk into the 'coffee', he... well, let's say that everyone heard him from down the hall. It wasn't pretty. The sound of coffee splashing everywhere mixed with his horrified gasp echoed through our open office space. I felt bad right away, though, his eyes were wide with shock and embarrassment. He looked at me in a way I couldn’t read... maybe anger? Hurt? I tried to apologize immediately but it just seemed to make him more upset. My prank backfired big time and now I’m stuck with this awkwardness hanging over us... After that, everyone kind of kept their distance, though no one mentioned what happened directly, just avoided the topic like walking on eggshells around Alex. And here I am, trying to figure out how to fix things without making it worse...