In my opinion, it's important not to use swearwords in forums where you don't know your readers personally. "douchebag" is mild but two of the swearwords you have used are strong ones.
There are some mild ones like "idiot", "fool", or some old-fashioned ones, amusing ones like "dunderhead", and "nincompoop". Inevitably, some people will feel offended by swearwords and your reputation would suffer.
"Retarded" is mild but could be offensive in context because originally the word was used as an insult for people with learning difficulties / mental handicaps.