How do I stop being so sarcastic and condescending?

I think you need to be humbled- clearly as shown by this you're pretty arrogant and immature. And usually this kinda thing transmits a vibe to everyone- not just these two people you've been focussed on. Being humbled will fix that up. Ever been to a hospital and see kids your age strapped up to IVs dying of disease? Volunteer- it'll be the best thing you've done for yourself. You'll learn a lot.