Spanish slang for calling someone ugly, hideous, can be used as an insult in any situation.
"you're face looks like it's been hit a thousand times!"
or less literal: "you're fucking ugly!"
The word "putaso" (singular) is extremely vulgar, and slang for "hit" ("putasos" is plural for "hits"). The word "putaso" should be used with caution, as it can be taken as a strong insult that can result in physical retaliation, and in Mexico, even death. If you wanted to call someone ugly without pissing them off too much, you may use something less vulgar, such as saying, "estas feisimo!" which translates to "you're very ugly!" which is less likely to result in being shot, kidnapped or beat mercilessly.