It does not mean what you think it means. If you are expressing amusement and simply must use a “z”, try “lolz”. If you are arguing on the internet, it is not analogous to “sadistic pleasure”. By incorrectly using it this way, you are watering its meaning down, and, in turn, making it less useful for everyone in the long term.
Stick to the canonical definition, as expressed by the cesspool of bile and occasionally excellent satire that created it. “Lulz” is the pleasure derived from provoking and/or observing unjustifiable internet rage. It represents a noble ideal of testing people and enforcing social norms. Be proud of the word. It is one of the most interesting concepts developed by the Internet's cultural elites, and now it deserves careful protection from the community that generated it.
Please, link others here. You may also peruse the other words and phrases nobody should say or ruin.
Disputes and suggestions may be directed to SuitCase (Email link).