Mejor Respuesta - Seleccionada por VotaciónIn case you don't know what 屌 is, it means penis. I guess it has something to do with phallic worship. Since we all know what a penis does and since it's used as an adjective here, I will personally translate it into "fucking good". Whether or not it's offensive is on a person-by-person basis.
PS
棒, meaning stick, is actually a euphemism for penis. Therefore, 你很棒 also means 你很屌, but it's not considered vulgar anymore.