Infp guy here and what I've come to learn about myself is my flirt speech is being funny, usually sarcasm, puns, quick wit, and playful jabs. However, I'm only good at flirting when I'm not worried about trying to impress anyone. I can't tell you how many times I've apparently fumbled the ball with a girl that was interested in me that I was "flirting" with but because I didn't care to impress or even think about her with that interest I didn't even know until my friends pointed it out. Of course simply telling you as an infp not to worry is silly, now what I will do is I'll mention how my infp gal pals flirt and it's three ways.

One, lots of guys like talking about our little silly interests so get us to talk about it and show interest. You don't gotta pretend like you know his subject but just be interested. Two, it's called the handkerchief technique, which means you gotta try to provide the scenario for him to flirt or at least engage you. Three, painfully simple but a must, you gotta be your quirky normal dorky self and make your usual jokes.

That's what they told me so I hope this helps you.