I remembered when I used to work in the office, whenever I talked to male counterpart over the phone, my female colleague liked to tease me and shouted at me:"Stop flirting on the phone!"
This reminded me of what I read here when RG flirted with the cashier girl (where he claimed the cashier girl started it).
Another incident, I used to patronize this Roast Duck, Char Siew stall at a coffeeshop. The guy who prepared and served the food over the counter always like to make fun of me. One day, I teased him back asking him: "Got goose meat? I want goose meat rice today." He was a little stunned and don't know what to reply. Haha.
Is that considered flirting?
I think it was quite harmless trying to joke and add spice to your day as long as you do not overdo it and make sure you choose the right person to tease and not somebody's husband or boyfriend.