Brazillians somehow managed to make an honorific pronoun became more informal than an "archaic informal pronoun" (more used in Portugal)

>tu acabaste
Tu is an informal pronoun, acabaste is a second person singular indicative past perfect cojugated verb.
>você acabou
Você is an honorific pronoun, acabou is a second person singular indicative past perfect conjugated verb.

Note : você must be followed with acabou, not acabaste.

However "você acabou" became a more coloquial sentence with time.