A young child who is extremely curious, sharp, and persistent, and who uses their cleverness to always get their way. (En español: Niño/a curioso e insistente que logra salirse con la suya).
That kid is such a pernéculo, he insisted so much that he finally got the ice cream. (Ese niño es un pernéculo, insistió tanto que al final le compraron el helado).