In Shakespeare's day, horns and antlers were a common symbol of a "cuckolded" husband, a.k.a. a man whose wife has cheated on him. So, whenever horns come up in a play, we know there's a 99% chance that someone is worried about starring in an upcoming episode of the reality show Cheaters.
Here's an example. When a lord kills a deer in the forest, Jaques says "let's present [the lord] to the Duke [...] And it would do well to set the deer's horns/ upon his head for a branch of victory" (4.2.2). Um, OK. Apparently, putting deer antlers on the lord's head sounds like fun, which is why all his buddies belt out a rowdy song in agreement:
Take thou no scorn to wear the horn;
It was a crest ere thou wast born:
Thy father's father wore it,
And thy father bore it:
The horn, the horn, the lusty horn
Is not a thing to laugh to scorn. (4.2.1)
"Wear[ing] the horn" is a reference to being cuckolded. According to this little tune, it's a common, age-old problem that's plagued generations of men. In other words, the song suggests that every single married man is bound to become a cuckold. According to Touchstone, age and social status don't even matter because all women are cheaters:
As horns are odious, they are
necessary. It is said, 'many a man knows no end of
his goods:' right; many a man has good horns, and
knows no end of them. Well, that is the dowry of
his wife; 'tis none of his own getting. Horns?
Even so. Poor men alone? No, no; (3.3.9)
Gee. Aside from being totally sexist and unfair to women, all this cuckold talk doesn't really make any sense because 1) nobody's been cheated on in the play, and 2) As You Like It is obsessed with marrying off all the couples. Why would a play that steadily works its way toward four marriages crack so many nasty jokes about cuckoldry? It seems like we have a major contradiction here, Shmoopsters. Let us know when you work it out...