Te llaman óxido ferroso.
[They call you iron oxide.]
This is funny because the chemical formula for iron oxide is FeO and “feo” means ugly in Spanish.
Another one, which works just as well in English:
Si feo volaba, serias rey de los buitres.
[If ugly could fly, you’d be king of the vultures.]
These came up somehow when I was trying to explain “yo mama” jokes to some Spanish people. They didn’t appreciate any of them which just goes to show that it’s okay to tell someone they hit every branch falling out of the ugly tree but messing with their mamas is a step too far.