I can never understand why some people always got something negative to say. or I can never understand why some people always have something negative to say.
Neither is wrong; this is what's called a difference of [register) by linguists:
In linguistics, a register is a variety of a language used for a particular purpose or in a particular social setting. For example, when speaking in a formal setting, an English speaker may be more likely to use features of prescribed grammar than in an informal setting—such as pronouncing words ending in -ing with a velar nasal instead of an alveolar nasal (e.g. "walking", not "walkin'"), choosing more formal words (e.g. father vs. dad, child vs. kid, etc.), and refraining from using words considered nonstandard, such as ain't. — This excerpt is from the Wikipedia page Register (Sociolinguistics) and CC-BY-SA 3.0 licensed.
"Some people always have ..." is the preferred form in formal registers, and in some informal register+dialect combinations. In other informal register+dialect combinations, "some people always got" or "...have got" would be preferred.
From another perspective, what's going on here is the beginnings of a language change: early modern English only permitted have in this context, but contemporary, informal spoken registers have begun the process of changing the preferred verb to got. Since the formal, written register of the language is slower to change, it still prefers have. (Note: I do not know how long got is attested in this context; this kind of change typically takes centuries to complete.)