Want to know if your crush likes you? Tell them a joke!
Psychology studies have shown that the easier someone laughs at your jokes, the more likely it is that they like you. They theorized that humor might have evolved as a way to indicate interest towards potential and existing relationships with romantic partners, friends, family members, allies etc. They say that people initiate humor to gauge the reaction in a new social circle, in the same way you dip a toe in the water before going for a swim.
So now you know... come up with the most horrible unfunny joke you can think of; if he or she laughs at it, then they're a keeper!