I'm going to assume you're talking about Robert Baratheon and not Robert Arryn.
He was a drunkard, a wife-beater, pined after some dead woman (whom he probably wouldn't have appreciated had she lived and married him anyway, considering the fact that he was fathering bastards left and right while he was betrothed to her) was so irresponsible that he probably attended like 3 Small Council meetings in the span of over a decade, and was generally terrible at his only job: Ruling.
If it's Robert Baratheon we're talking about then I don't hate him! I actually find him funny at times... other times though he is just a drunk and only talking drinking, killing and women those times I don't like him
Robert Baratheron was a legend! Yes, he may have been prone to drinking the odd vat of wine here and there, constantly cheating on his wife and fathering countless bastard children and not giving a damn about the kingdom, but he was a good man deep down. Joffrey his (son) didn't really drink, didn't foster bastards and was keen to rule. But he was a bit of an evil git.