These two expressions are high on my hate list. I use them relatively often, too. So, if I dislike them so much, why do I use them at all?
To me, they signify some sort of defeat. Whenever I hear someone — even myself — utter them I imagine they have met an obstacle that prevents them to continue whatever they were doing. Saying “oh no” and “uh oh” means that you have acknowledged something that stands in your way, something that might be too big for you to surpass. Does that mean you are a coward?
Well, it depends. However much I hate catching myself saying “oh no” to even the smallest thing, I genuinely believe that this phrase can be a means to find a new strength or motivation to accomplish your stuff. When you do something stupid, “oh no” can serve as an acknowledgement of your mistake. Yes, you made something stupid and now it’s time to either forget it or analyse the situation and rectify it. The key action is to be forgiving and accepting. You cannot grow if you give up or worry about your mistake so much that it prevents you from functioning in a normal, constructive way.
“Oh no” and “uh oh” might not be such bad phrases after all, you just need to be kind to yourself and believe in (self-)improvement. However, don’t let them define you or else you risk to see everything you ever do as a series of mistakes and not steps towards a better you.