I can't think of an idiom that does all three of these things:
I have a few idioms that do parts of what you ask. Consider this a partial answer.
Make a decision all by yourself without involving or consulting others: he put the cart before the horse (suggesting he mixed up his priorities) or got ahead of himself (suggesting he took a premature action or insufficient information). Neither works by itself for your intention - there's nothing in either one that requires others' feedback to right the cart or make the action mature.
For disregarding feedback, there's little better than a tin ear. It is often applied to people who can't appreciate the subtleties of music, but "tin ear" is also applied to people who disregard another's attitude or mood. Other idioms might include turn a blind eye or shut his eyes to, which both involve ignoring or refusing information that may be inconvenient. The disadvantage of all of these is that none of them need pertain to decisionmaking, nor do they restrict the attitude of the people being ignored.
If he assumes that you will accept it, he is taking your consent for granted. In other words, he expects your acceptance. This requires incorporating acceptance or consent as the object of the phrase, and of course it doesn't entail anything else you want it to mean by itself.
This is a partial answer because all three of these idioms together might work, but it'd be pretty weird and idiosyncratic, and perhaps better idioms exist. Here's an example of what combining them looks like:
With this latest decision, Jonathan got ahead of himself, turned a blind eye to his coworkers, and took their acceptance for granted.
On second thought, it felt like I needed to specify "decision." If I do that instead of using the first set of idioms, maybe this would also work:
With this latest decision, Jonathan turned a blind eye to his coworkers and took their acceptance for granted.