Is there an action, sans context, that is de facto irresponsible? I feel like a few should jump to mind immediately. But when I think about them for any length of time, I can imagine a rare justification for even the most imprudent-seeming behaviour.
Spending a fortune on a car would be silly for a person with a £50k a year income, but expected of a millionaire. Sex without a condom is sane if you want and can support children.
Unfortunately, what I notice is irresponsibility inversely scales with income. The wealthier you are, the more likely an action could be called responsible. A £200 dinner is fine if you're middle-class and moronic if you're on welfare. Even health risks are defensible if you can afford the healthcare.
This sort of sucks. However, moaning about it changes nothing. Given the reality, we each need to adjust to our situation. If you're poorer, you have to be more responsible. Perhaps the worst thing about this is scientific evidence points in the opposite direction: the poorest usually have the lowest impulse control. The cruelty of life, eh?