The structure 不…才怪呢 and 没…才怪呢
The structure 不…才怪呢 
and 没…才怪呢 mean "it would be strange, if not...". They are used to express confidence in a result.
For example, the phrase
他不满意才怪呢 implies that he is “should be happy”.
and 没…才怪呢 mean "it would be strange, if not...". They are used to express confidence in a result.
For example, the phrase
他不满意才怪呢 implies that he is “should be happy”. Pay attention
The particle 没 is used before 有 or other words beginning with 有.
In the structure, the ellipsis is replaced with a verb predicate.
Scheme
subject
不/没
predicate
才怪呢
Examples
他要是不知道才怪呢
It would be strange if he didn’t know it
tā yàoshi bù zhīdao cái guài ne
星期天还得加班，大家没意见才怪呢
They must work on Sunday! It would be strange if nobody had complaints
xīngqítiān hái děi jiābān, dàjiā méi yìjiàn cái guài ne
妈妈知道的话，不生气才怪呢！
If my mother found out, it would be strange if she didn’t get angry
māmā zhīdao de huà, bù shēngqì cái guài ne
The negative determiners 不 and 没 can be omitted. The phrase 才怪呢 can be used by itself in the meaning of "it would be strange...".
Examples
这么差的服务态度，顾客满意才怪呢
This service is so bad! It would be strange if guests were happy
zhème chà de fúwù tàidù, gùkè mǎnyì cái guài ne
明天出发，你现在才想起来了订机票，能订到才怪呢
You are supposed to be setting off tomorrow, and you have just remembered to buy a ticket. If you manage to do it, it would be surprising
míngtiān chūfā, nǐ xiànzài cái xiǎng qǐlái le dìng jīpiào, néng dìng dào cái guài ne
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