I think whether you are a new nurse or have been working as a nurse for a long time coming now, one of the hardest things to deal with in itself is not the patients but those you work with.
I put myself in your shoes and the above situation you told us about. Probably the aggravating thing here is how he probably thinks it's OK for him to act the way he did just because of how long he's been working there. I can't say this for sure but it seems like it is easy to get a few passes for the way he acts around the unit just because he's been there for so long. To me, personally, his reaction was inappropriate and in any situation like what you had to deal with, no body should be coming into a room and saying that to you in the first place...even if you did misplace it, he could come back later and tell you when things have calmed down. How was him saying that at that time and place helping the situation? If he knows and can easily put the tank elsewhere, he should have done so without all that commotion and approach you later.
You also have to understand that it's hard for other people who don't have the same title as you do, to understand your role as a nurse. I appreciate the majority of my CNAs around my hospital, and know I wouldn't be able to last through the day without their help, but there are some who I feel really don't understand the RN's role as a nurse. When I was still externing at my local hospital, we had a confused and SOB patient who did not follow any given instructions and kept getting in and out of bed to use the bedside commode next to his bed when we told him not to by himself (I was the one who put this next to his bedside in the first place). I ended up putting the bedside commode back in his rest room to prevent him from getting up and to instead call for help. Maybe I could have handled this a different way (had someone come stay with him, leave the commode at the bedside) but he ended up walking with an unsteady gait to the restroom to use the commode without assistance. The problem was the CNA saw this entire thing.
I had no idea what the CNA was trying to do but she called both me and the RN I was assigned to for the day to come to the room. I got there first and she said to me "He almost fell down because YOU put the bedside commode back into the restroom!. And when she called my RN on the phone to come, all she said to my RN is, "Look, come look how he's walking!" Instead of worrying about the patient falling and getting the patient back to his bed right away, her focus was for the nurse to see how he was walking. The RN and her had a go at this and it was not pretty.
Writing this story just so you don't feel like you are the only one who have to deal with situations like these. To me, one of the hardest things I have to deal with is gaining respect from those who you can delegate to that have worked there longer than you have. I am a new nurse and I am also much younger than many of the LVNs or CNAs so I know this is a tough challenge to gain for me.
I hope you have talked with him and resolved the situation. Good luck.