(My native language is not English) You describe a scene in a movie or book to someone else. when talking ... it's a lovers quarrel. ... it's a lover's quarrel. ... it's a lovers' quarrel. would sound the same. But when writing? I think I know the difference. lover's ... a quarrel owned by one lover (he/she quarrels with him/her self) lovers' ... a quarrel owned by two lovers lovers ... no owner, the quarrel, it's just a quarrel between two lovers So, what's the proper way to write this? I think lovers' feels best, but....
A quick googling tells me that it's definitely regarded as a possessive construction, so lovers as a simple plural noun serving as an adjective is out. Both singular and plural seem used in the possessive construction. The OED prefers the singular.
I've always written it as lovers' quarrel, since by nature it involves two people. But I can see the reasons to punctuate it the other two days :/