Inconsiderately means in a thoughtless way toward other people — doing the inconsiderate thing. You use it to describe how someone acted, not what they are as a whole. Speaking inconsiderately, driving inconsiderately, treating a guest inconsiderately. It is a little more formal than just saying “rudely” or “without thinking,” and it keeps the special meaning: the problem is that other people’s needs were not in the picture. Though actually, “rudely” can be about tone or manners; “inconsiderately” is about not taking others into account, even if the voice was polite.