In addition to this, some examples in context:
"Ich mache doch nichts kaputt!" - "Why are you telling me not to touch your computer? It's not like I'm breaking anything", or "Come on, there's no reason you shouldn't let me touch your intricate artwork, I won't harm it, you know", or "Why are you laying me off this job? After all, I don't break anything, I often come to work on time, and hardly any customers complained!"
"Ich mache doch nichts kaputt?" - "I'm already pulling very hard on this lever; I'm not breaking anything, am I? / are you sure I'm not breaking anything?"
Duo doesn't like "After all, I'm not breaking anything." with "I'm" appearing to be the problem. Will report it so the answer database can be expanded. Is "After all" acceptable for "doch" in this sentence? or is "doch" an emphasizer that doesn't really translate to English?
That's the right idea, only the phrase/word is "kaputt machen / kaputtmachen":
"Ich mache meine Tasse kaputt", "Ich werde die Tasse kaputt machen / kaputtmachen", "Du hast meine Tasse kaputt gemacht / kaputtgemacht!"
I'd imagine "kaputt machen" to mean that the object is, on the whole, quite "destroyed" afterwards, like a smashed cup or window, a torn-up shirt, a squashed bug, a computer that won't work anymore.
Just "kaputt" as an adjective doesn't have to mean "destroyed", it's also for damaged objects like clothes ("meine Hose ist kaputt" can mean that there's a small hole in my trousers), or for objects that have ceased to function / have a malfunction, e.g. cars: "Mein Auto ist kaputt" = my car doesn't run [properly] anymore because a) it got totaled by a train / b) it won't start / c) a little lamp tells me that the airbag needs a repair.
As per Bettilda's remark, "after all" is an emphasizer in English, and it seems to me to function like the "doch" in the German. We could also say "But I'm not breaking anything", where "but" is an emphasizer, not a conjunction. See the difference between these scenarios: (1) "I'm juggling ten glasses, but I'm not breaking anything!" Here, "but" is a conjunction. (2) "Please don't touch my delicate sculpture," "But I'm not breaking anything!" Here, "but" is an emphasizer.