"Beg" is UK/London youth slang for a person who is a sycophant, desperate for
attention, or someone who's so deep into a parasocial
relationship they've lost all sense of themselves that they're
chronically online kissing the ass of their idol and all their family members' while also informing randos about them in dms.
A "beg" (or someone "begging it") tries too hard to fit in, sucks up to others, or acts in a pathetic, desperate manner to gain favor.
It is often used to describe someone copying others, stealing other fans' work to pass off as their own or chasing clout.