Japanese as a language relies very heavily on politeness and formality. I was telling Polnareff not too long ago about the different words for 'I' and how they vary in formality. To use the same example, I ordinarily use watashi or boku because those are more or less the accepted standards for someone my age. The former is more or less default, while the latter is slightly more casual. Jotaro, on the other hand, uses ore which is about as rough and informal as you'd expect from him.
More to the point, with a language such as that the simple absence of formality is essentially a massive show of disrespect. It's not difficult to insult someone completely by mistake, if one's not used to speaking it. Continuing to use Jotaro as an example, I think one of the first things I ever overheard him saying was やかましい, 'yakamashii', which is basically 'shut up'. Which doesn't sound like much as far as insults go, but I suppose the tone may not translate well.
To use another example, the word for 'you' we used to refer to each other that day was 'きさま', 'kisama'. It's a rough word that is probably better translated as 'you bastard' or something to that effect.
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More to the point, with a language such as that the simple absence of formality is essentially a massive show of disrespect. It's not difficult to insult someone completely by mistake, if one's not used to speaking it. Continuing to use Jotaro as an example, I think one of the first things I ever overheard him saying was やかましい, 'yakamashii', which is basically 'shut up'. Which doesn't sound like much as far as insults go, but I suppose the tone may not translate well.
To use another example, the word for 'you' we used to refer to each other that day was 'きさま', 'kisama'. It's a rough word that is probably better translated as 'you bastard' or something to that effect.