The description of what you want doesn't really seem to fit your example.
There is a German idiom related to what you described: "Wenn es dem Esel zu wohl wird, geht er aufs Eis". (Literal translation: "When the donkey gets too comfortable it walks onto the ice.")
It's relatively easy to translates German idioms into English using online sources, but in this case the only thing I could find was: "Complacency makes one reckless". It has the same meaning, but it's much more abstract.
There is also a German idiom that doesn't really fit your description but comes very close to the idiom you used in your example, and so does its English translation:
"Er hat Hummeln im Hintern" - literal translation: "He has bumblebees in his posterior" - English idiom: "He has ants in the pants".
Finally, you may also be interested in a simple adjective/adverb and noun related to both situations: wanton(ly) and wantonness. It's a legal term used for doing something bad intentionally rather than negligently.
Also capricious(ly) and capriciousness for the more harmless, less destructive variant.
Putting it all together, I offer the following variations on your example:
- Complacency makes one reckless, so he went to the cinema. [Since it was at the other end of the city and his foot was still swollen, he had to call a taxi when it was over.]
- He had ants in the pants, so he went to the cinema. [Nothing bad happened.]
- He wantonly went to the cinema. [So the Americans bombed the cinema, as could be expected since he was carrying Osama Bin Laden's mobile phone. 35 'terrorists', 24 women and 43 children died. He was one of the few survivors.]
- He capriciously went to the cinema. [When he returned, his wife nearly killed him, saying he was a worthless bastard.]
I have included typical examples showing how you would use each word or phrase. The connotations are really quite different.