My favourite is

         Aşağı tükürsem sakal, yukarı tükürsem bıyık

´If I split down, beard, if I split up, moustache.´ It´s used about a no-win situation. Maybe my thinking is too visual, but it always makes me smile.

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Oh, I´m sorry. I just noticed there was a post about it already.

One English expression is ´missed the boat´ if it´s a missed opportunity. ´I/you/he/we missed the boat´ but its not really used to make fun of someone.

Yılanın başını küçükken ezeceksin - Kill it before it grows

Is there such a saying in English?

 "To nip something in the bud" ... like the Turkish it implies that the thing you are stopping is a negative, unwanted thing.

Here´s another similar saying:

Son gülen iyi güler = He who laughs last laughs best

Sert kayaya çarpmak - to hit a hard rock

 Another similar pair:

To shut the stable door after the horse has bolted

At alını çoktan Üsküdar´ı geçmiş

 we say, "to hit a brick wall"

guess our saying was invented by a city-dweller, the Turkish by a villager