Can 牛 be an insult?


In a manga, while a guy was sleeping, someone used a marker to write on him.
He wrote `牛` on his forehead and `空回り人生` on his chest. Considering it was a
joke, can `牛` be offensive or funny in some way? I think that `空回り人生` could
mean something like `loser`, but I don't understand why he wrote `牛`. It is
neither a reference to the personality of the character nor to the plot of the
manga.

I know `cow` can be an insult in English, but what about Japanese?

You can see the page in question [here](https://i.stack.imgur.com/NieGl.jpg).




I think it depends on the context. But maybe...

In キン肉マン(kin-niku-man), an old famous manga, many heroes have a kanji on their
forehead. Be affected by this manga, writing a kanji on the sleeper's forehead
became a common prank in Japan. Typically, the kanji is [肉]{にく}(meats),
because this kanji is on the main hero's forehead.

Next, there is a proverb 「[食]{た}べてすぐ[寝]{ね}ると[牛]{うし}になる(If you go to bed as
soon as eating, you'll become a cow.)」 in Japan.

So I guess:

Why a kanji is written on the sleeper's forehead? --> Because it's a common
prank with the sleeper in Japan, as drawing eyes on the eyelids.

Why the kanji is 牛? --> Because he is sleeping (if he went to bed just after
eating).

Of course, if a cow has a special meaning in the manga, the kanji 牛 may also
has a different meaning from my estimate.




I think it depends on the context. But maybe...

In キン肉マン(kin-niku-man), an old famous manga, many heroes have a kanji on their
forehead. Be affected by this manga, writing a kanji on the sleeper's forehead
became a common prank in Japan. Typically, the kanji is [肉]{にく}(meats),
because this kanji is on the main hero's forehead.

Next, there is a proverb 「[食]{た}べてすぐ[寝]{ね}ると[牛]{うし}になる(If you go to bed as
soon as eating, you'll become a cow.)」 in Japan.

So I guess:

Why a kanji is written on the sleeper's forehead? --> Because it's a common
prank with the sleeper in Japan, as drawing eyes on the eyelids.

Why the kanji is 牛? --> Because he is sleeping (if he went to bed just after
eating).

Of course, if a cow has a special meaning in the manga, the kanji 牛 may also
has a different meaning from my estimate.

