Poner Los cuernos

Means "to put the horns on". When someone puts the horns on their significant other means they cheated on them. They "made a fool" of that person. A guay (way) is an ox or slow dumb animal made for work. When you "put the horns on" your spouse, you turned them into a guay. It is an insult to call someone a guay, or say that someone is putting the horns on him. It's worse than calling a man a fool, but more like...he's being "played for a fool". It's a deep insult to call a Mexican Male a guay or say "te va poner los cuernos" because it not only emasculates the man, but it's insulting his lady as well bu insinuating she is a cheater/ho/slut/whore/puta. This is why Mexican women will cut a guy who calls her man a "guay"...or says "te puso los cuernos". It is now used casually like fucker and dick are used instead of saying dude, or homie. Ex..."Hey fucker, we gonna hit the club tonight?" It isnt calling him a real "fucker" but in place of dude. Same way "guay" is used. Ex. "Hey Guay, vamos al baile o que onda?"