According to definitions being sinister is rule breaking or being evil. I occasionally read of Satanists talking about being sinister, as if this is a commandment that in order to be Satanic they must break every rule going.
In my opinion being evil is a human judgement of others, who say you broke their rule thus you are evil. In essence being of a sinister nature, you break the rules.
I consider that Satanism is about manifesting your will as an individual. If a Satanist is driven to need to break rules in order to validate their label, that in my opinion is not Satanism, rather they are trapped in a delusion that undermines their ability to be an individual.
Rules in my opinion are useful, they provide boundaries in which I can work in whilst I manifest my will as an individual. I like playing chess, so I prefer you playing chess according to the rules, which makes chess a fun game of skill and strategy. Rules of science such as gravity offers you the insight that if you jump off a cliff gravity will injure or kill you. Rules of business contracts makes it possible for me to run a profitable business knowing I will be paid for work done. Rules of language means I can communicate with you in an understandable way. Rules are a tool by which the individual can conduct their lives efficiently and productively.
If a decision maker makes a rule that in its nature is unjust, undermining my ability to manifest my will as an individual, then I am going to oppose or break the rule. I do not go out of my way to break the rules, I consider each situation as I find it, then I act accordingly.
It seems a common observation that when I see Satanists boasting how sinister they are, reacting to rather than using the rules to their advantage, I note their circumstances such as unemployment, prison history, low paid jobs, a biography of failure and social rejection, because they failed to realise that rules are opportunities to prosper rather than holes to fall into through mindless rule breaking, triggering the penalties hidden inside the rule.