What are the rules of writing a 对联 (chinese couplet)? I have looked at the Wikipedia article &quot;Couplet (Chinese Poetry)&quot;, but I think it poses more questions than answers.
So a 对联 (duì lián) is a &quot;Chinese couplet&quot;:

it is composed of two lines;
each line must have the same number of characters;
the characters on each line must have a correspondence with each other;
the characters on each line must have opposite &quot;tone pattern&quot; (平 vs 仄).

If a 平 tone is a &quot;first tone&quot;, and all other tones are 仄, then the Wikipedia example doesn't make sense (qín wéi is 平?).
And I'm unclear as to whether each &quot;character&quot; must be related, or each &quot;word&quot;?
For example, 很贵 and 便宜 have opposite meanings as words, but not as characters.
As an example, is this a 对联?

猪扒便宜 Zhū pá piányi
鸡腿很贵 Jītuǐ hěn guì
平仄 can not be understood by a Chinese who only speaks Mandarin or some dialects, as I mentioned in my answer to the previous question "Different kinds of writing in Chinese". In mandarin, in many cases, 平 refers to the 1st and 2nd tone. 
The pattern of 对联 derives from the classic poems, a word-match is enough.
Nowadays, we usually write a 对联 at a celebrating time, e.g. the spring festival, or on the day when you get married, etc., and paste it besides the gate of your house to celebrate the event. As it is written to celebrate something, the content usually refers to good things like "be fortunate, be lucky, be happy, be healthy, etc.", so I think your example would not be considered as a 对联. Of course, you can use it in a humorous way, but I think you won't paste it.