"If you're good at something, never do it for free."
Rapboat's mom charges $5 a blowie.
Rapboat's Mom
Explanation
Explain Bear
Alright, listen up, buttercup. The joke is, someone said if you're good at something, you shouldn't do it for free. Then, they imply that Rapboat's mom is good at giving blowjobs, so she charges money for it. See, it's funny because it's unexpected and kinda vulgar. I bet you didn't see that coming. I do!