I'm confused here. Posting "LOL!" is not spam in any way, at least how i define spam. It might not subjectively be appropriate (if it's not appropriate to find it funny), it's debateably irrelevant (if it is not important who finds it funny). But it's not spam.

Spam is broadly defined as unsolicited bulk advertising. An example spam comment would be "LOL! Also check out this great pharmaceutical company: xxx".

The latter is certainly something that should be filtered out, if it's irrelevant advertising that marketers are using to peddle their crap. It's mostly unsubjective and uncontextual and its appropriate for filters to automatically detect.

But filtering out the former is a form of censorship that is often best left to humans (like downvotes to bury bad comments). I don't think this should be the job of the comments system to determine what is considered "appropriate" or "beneficial to the discussion."

A "LOL" or ASCII art image or "no u" or any other meme can be anything from a well-timed ironic offhand jab, an appropriate affirmation or response, to totally irrelevant and inappropriate noise. It depends on topic, context, parent, and existing noise in the thread and is inherently objective.