Internet clichés.  Specifically, the rather predictable responses that are so frequently trotted out on discussion forums.

Some tend to be specific to a particular type of site, such as, on social networking or dating sites, it will often only require a few minutes between somebody starting a thread complaining about being single, before another user will tell them one or more of the following:  Seeming needy isn't an attractive trait; you can't love somebody else unless you love yourself; relationships aren't all they're cracked up to be; it's better to be single.

Similarly, a bad luck story in a support forum will almost certainly quickly produce a post from a contributor telling them they should think themselves lucky, and either: a) go on to mention a far worse experience that they went through and survived, or b) tell the original poster not to be so selfish, and to think of all the people in the world who are less fortunate.

Some are more general - a lot of forum users, for instance, are familiar with Godwin's Law regarding the tendency of internet forums to end up in references to Nazi Germany.

The first point about all these, like the majority of clichés in all probability, is that they are largely true.
The second point, is that, by and large, in the context of an discussion forum, they're absolutely no help whatsoever.
The third point, is that they're the grist to the mill of most forums, which would be duller places without them.

So I was delighted to discover a new, emerging cliché - in, of all places, a discussion board on an acting jobs website.  I've seen it about three or four times now. It runs like this:
Somebody starts a thread, asking about an item of acting technique: Specifically, how to cry on cue on an occasion when, for whatever reason, the tears won't come.  There will be a smattering of posts about "tear sticks", onions, pepper (!), Vicks vapo-rub, etc. And then, always, without fail, some bright spark will say that using these aids is cheating, and that they should try acting.  Always.

Ticks the boxes nicely:  Is it true? Yes it is.  Is it any use to anybody? None at all.  Will it incite the other posters on the thread to expansive gestures in defence of the original poster?  Damn straight :)

A rather specific example, certainly, but I felt a sort of warm, patronising glow at the thought that a comparatively young set of discussion boards had somehow come of age. 

The same set of forums now has the beginnings of a major rant at the owners of the site about a tiny unsubstantiated rumour related to data protection.  I'll get the popcorn.