"Ser un huevón(a)" = To be a big egg*

More "eggy" expressions ;) If you are told to be a "huevón" o "huevona" is because you are a very laid-back, slow and even lazy. Sometimes, the expression gets "harder" and you can be called "huevo duro" (hard-boiled egg). That is a step beyond in describing you, as you have been promoted to the status of "thick".