A wisecrack is a funny joke or a sarcastic remark that makes someone laugh. The class clown is usually famous for their wisecracks.
You can use this informal word as a verb, too: "How can I know when you're serious if you just wisecrack constantly?" Wisecrack first appeared at the start of the 20th century, from a now-uncommon sense of the verb crack, "speak loudly or boastingly," which is also used in the phrase "to crack a joke." It takes more than wisecracks to be a successful comedian, but it's a good start!