All of the extremely dirty words in English are monosyllabic (some examples). It's always been funny to me that there were certain grunts we can utter that make people uncomfortable and make children giggle and blush.

I always figured there must be some words like these in Chinese. They would have the added bonus of having a single chinese character, i.e. a picture that would make people uncomfortable. When I'd ask my Chinese friends, the closest they'd give me was something that translated to “his mother” or “your mother”. These were no good because

• They use two characters.
• The characters themselves aren't inherently bad; the phrase is dirty. This is equivalent to saying someone sleeps with their own mother. That's not a swear word, it's an insult.

As it turns out, my Chinese friends were being coy. There is a single character — a picture — a single flat-toned syllable that makes Chinese speakers blush. It is bī.

This word is funny on many levels.

• It's an inherently dirty word as it's a vulgar word for female genitalia.
• It's made from the characters for ‘body’ and ‘cave’ stitched together.
• Combined with the word for ‘cow’ (níu), it means ‘cool’ in a cocky, aloof way.
• Combined with the word for ‘stupid’ (shǎ), it's derogatory. “You stupid female genitalia!”

References:

• The Unspeakable bī
• Essay about Chinese swearing
• Essay about swearing at soccer games
• Wiktionary entry
• 屄.com