The thing about safe spaces is that they're not about being places where you're not allowed to offend anyone. They're about providing somewhere safe and secure for particular groups of people. If you're going to organise safe spaces you need to do them effectively.
It's like having a support group.
For example, sexual assault or rape survivors may find it difficult to navigate every day life sometimes because of the things they hear. A lot of people say quite harmful things, joking or not, without being aware that quite a few people around them are affected by the subject. Safe spaces should be about allowing a specific group to enter a room or area where they know others are similar to them and won't use the language or harsh jokes that others do. They can all agree not to talk about it there.
Safe spaces should not be about punishing people for what they say. It should be about allowing affected groups to have a sanctuary they can feel safe. It's just common sense that if you enter a safe space for sexual assault, don't make a rape joke. If you enter a safe space for depression or self harm, don't discuss depressed people or self harmers cruelly. If you enter a safe space for a specific race, don't rattle off negative statistics about them or make them feel inferior to you.
If you don't feel comfortable behaving this way, don't enter the safe space. The safe space should never be a place that is necessary to go or pass through, like a library or public area.
Safe spaces are not about SJW's sitting in a circle and jumping down your throat for saying something politically incorrect. Or at least - it should not be and was never intended to be.