By asking them "Why?"

You never know, they might just be Canadian.

"I'm flirting with you,"

"Why? Don't lie to me." Whilst I'm making a mental list of absolutely everything why that's complete bollocks

I had a girl in high school (high school!) literally say to me "when am I going to get to feel that dick of yours inside me?" and I blew it, thought she was just joking.

Imagine a girl you like putting a hand on your shoulder, looking into your eyes, saying some gentle word I don't quite remember due to being mesmerized by those eyes, and you know what I did? I just looked back uneasily for a few seconds, then nervously took her hand off my shoulder, shook it a bit, released it and awkwardly smiled. (That even wasn't her last attempt to make me happy against my best efforts ; ended bad anyway.)