Examples:

• After his promotion, John started acting high and mighty, ignoring his old friends.
• Sarah’s tone changed completely once she got a new car—she acted high and mighty, as if she was better than everyone.
• Don’t act all high and mighty just because you know a little more about the subject than I do.
• She acts high and mighty at work, but everyone knows she’s not as knowledgeable as she pretends to be.
• Tom started acting high and mighty after winning that award, but people quickly grew tired of his attitude.
• The CEO acted high and mighty, refusing to speak to employees lower down in the company.
• Just because you're the team leader doesn't mean you have to act high and mighty with us.
• When we disagreed with him, he began acting high and mighty as if his opinion was the only one that mattered.
• She loves acting high and mighty at parties, always name-dropping and talking about her wealth.
• Ever since she became a manager, she’s been acting all high and mighty, forgetting where she came from.
• He tends to act high and mighty when discussing politics, making others feel inferior for their views.
• My neighbor acts high and mighty because of his expensive house, but no one is impressed.
• You don't need to act all high and mighty just because you’re in charge for the day.
• During the meeting, she acted high and mighty, dismissing everyone else’s suggestions.
• He acted high and mighty in front of the new employees, making them feel uncomfortable.
• She started acting high and mighty after receiving compliments from the boss, but it didn’t last long.
• His constant need to act high and mighty is pushing his friends away.
• Don’t act high and mighty with me—I know you’ve made the same mistakes before.
• He walked into the room acting all high and mighty, but no one took him seriously.
• She acted high and mighty when discussing her education, but it only made people resent her.
• In this sense, being awarded with the Oscar had not caused him to act high and mighty.