Recap:
"i dnt beleve u cuz u r grill(sic)"
"no fuk u"
Nothing to see here, people.
Also after a few seconds of research I was proven wrong, it looks like "damnit" is the "improper" spelling of "dammit", which is the phonetical spelling of "damn it".
Damn it.
I'm so confused now.
Yeah but 'dammit' is a bastardization of 'damn it' in the first place, I don't think it's officially a contraction for it:
From MW:
Origin of DAMMIT
alteration of damn it