Offline swearing is generally a lack of discipline in sustaining your emotions. It's a weakness, and shows you're not capable of expressing your position properly with common words. Swearing is the easy way out, but it gives people around you a negative feeling about you (could be sadness, anger, pity). Not judging anyone who does, for I'm swearing too sometimes.

Online swearing is plain childish, as you have all the time to think of a proper way to explain yourself.
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