1) Marrying the pregnant (oftentimes unmarried) sister of the girl you love...e.g. Karan marrying Lata. This happens all the time...actually it's quite FASHIONABLE to do so! (Trishna/Tanya/Raj, etc. And let's not forget the Manav--Archana--Choo "love triangle" on PR.
2) One person marrying but in love with a person from the other couple (Trishna/Tanya/Raj) and IN THE SAME CEREMONY. Like Abha/Sanskar marrying right next to Karan/his friend.
3) Living under the same roof -- characters from #2 above to boot!
4) Killing off 1/2 of an extremely popular jodi (Karan/Lakshmi in Ghar ki Lakshmi Betiyaan), I think out of spite for the person playing the part. Don't even think of this...not now or later.
5) Karan has an evil twin
6) Getting your sibling to marry, pretending to be you. Technically, it does not count! (Choti Bahu)
7) Making sacrifices for no reason aside from it's just a thing to do, especially when viable alternatives exist! (Agle Janam, Choti Bahu...I think I may have to list all the present and past Zee shows!)
8) Good brother--bad brother living in same house as crazy, control-freak dad (Agle Janam, and oops, it's in MGGK)
9) Female lead protagonist doesn't run, goes up in flames and jumps into river, only to come back to family year later looking completely different, no marks and all. (Kasam Se)
10) Nothing destroys a marriage like trying to kill your wife's dad (Ghar ki Lakshmi Betiyaan). As tempting as it may be (Jagmohan, Thakur), it may cause misunderstandings 😆...it's a total deal breaker, folks.
11) Falling in love with your brother's wife (Maayka) and ultimately, marrying her since she is....(drum roll) pregnant with brother's child. I don't think we need to worry about this in MGGK!
12) Sister marrying look-alike of her older sister's evil husband. Again no twins! No triplets either!
Feel free to add to the list.