I treat people the way they treat me. So yes, I'm very nice. But if you faaak with me, I'll slit your throat. Figuratively, not literally...not literally cos I wouldn't survive 5 minutes in jail :)
Yes. I think it's catching. If you leave someone with a good feeling, they are more likely to be nice to the next person they meet, or have a slightly better mood for a while. I think it applies in many situations: courtesy and giving way on the roads, a chat with the check-out chick in the supermarket, offering help to strangers if they need it, listening when someone needs to be heard, not expressing criticism or negative judgements but finding neutral ways to express differences... and so on. But if someone is not nice to me, I will politely exit and generally avoid them in future.