conc▪ Like also (post-classical) ↗šarrābaẗ ~ šurrābaẗ ‘tassel’, šārib ‘moustache’ is usually regarded as derivation from ↗šariba ‘to drink’. The semantic relation however is nowhere explained convincingly in detail and remains rather doubtful.
▪ Therefore, instead of trying to link šārib and šarrābaẗ to ↗šariba, is it not possible (and also more likely) that we are dealing with reflexions of another etymon here? I suggest to put both together with ↗ĭšraʔabba ~ ĭšrābba ‘to stretch/crane one’s neck’, which seems to be cognate to lHbr širbēḇ ‘1 to stretch out, prolong, enlarge; 2 to draw down, let down’, Aram šarbēḇ ‘to prolong, let hang down, let down’, Š-stems belonging to the complex of Sem *rabb‑ ‘big’ (cf. Ar ↗rabb ‘lord, master’). šārib ‘moustache’ as well as šarrābaẗ ‘tassel’ could then be explained as *‘hanging down, projecting, overhanging’. The unusual phonology—the regular correspondence would be (Sem *š >) Hbr š, Aram š ~ Ar s, and (Sem *ś >) Hbr ś, Aram s, Ar š —could be explained as the result of a late development. – Should it be possible to corroborate this hypothetic etymology, then also ↗mašrabiyyaẗ may have to be reconsidered, see s.v.