Using 'high and mighty' implies a judgemental and scornful attitude towards someone's behavior. Don't talk to me in that high and mighty tone; we're equals here.
Pro Tip 2/3
Sarcastic Usage
'High and mighty' can be used sarcastically to mock someone who is being overly proud or arrogant. Oh, excuse me, your high and mighty-ness, didn't realize you owned the place!
Pro Tip 3/3
Informal Context
The phrase is often used in casual conversation rather than formal writing or speech. She's acting all high and mighty now that she won the lottery.