The following lines could be great if you're trying to flirt with your crush for the first time. These gentle lines are mostly complimentary or flattering. So, even if they end up not being interested, they still might be appreciative. Who knows, your friend may be too shy to flirt first, and these are a great way to see if a spark is really there.
Gently touch the meat thermometer to their arm, look at it and say, "Huh, it says here that you're like super hot."
"I know this is Friendsgiving, but what does it mean if my crush is here too?"
"Wow, this [insert dessert here] is sweet. And so are you."