Lying is generally disgraceful. You don't follow a path in the name of Truth(Satan) and go around lying to everybody. There are very few circumstances where lying is acceptable, like pretending not to be a satanist in order to keep yourself safe around those who are without.
There are also times when you might not be 100% honest because it keeps the peace and prevents offending people unnecessarily. In other words, white lies. This is more palatable and acceptable in society.
Lying is otherwise generally destructive and fosters distrust and contempt in society.
Gossipping is generally an andrapoda activity, but it can be part of the bonding experience between people. Use your discretion but try not to gossip about people, it's disrespectful to talk behind people's back and violate their privacy.
Swearing is in the same vain. It can be used for emphasis but I say try not to use it, it's a mark of lower intelligence and lower class to swear casually.
It is not forbidden to do any of these things in Satanism but use your discretion and try to be a kind, constructive and respectful person.