sedevacantism is odd, however, the expression opens the door.
Example: When explaining to others that we are Roman Catholics who hold to the position of sedevacantism. Most will say ... "what is that?"
At that point you can teach them the truth about the "pope" of today and why he makes headlines every day with his strange teachings, such as baptising aliens, urged priests around the world to be more accepting of gαys and ... downplays the idea of "living in sin" and suggests that priests should use their own discretion on whether divorced Catholics in bad marriages can take Communion, and other things like the Vatican admits they own the giant telescope named LUCIFER.
We can tell them that sede vacant means the Seat of Peter is currently without a True Pope sitting there. We can tell them that the current pope has adapted to the world, and makes man the god, by changing all the practices and teachings that the past popes have taught, are now for the benefit of man, not God.
The most important issue we can teach them is that the Church is still here, the gates of Hell have not prevailed, it is just smaller now. We can tell them not to be scandalized by what they read in the newspaper anymore of how the Catholic church has changed because it really has not; it is the robbers who now hold the property of the Catholic church, who are pretenders in wolves clothing that are in control by changing what appears to be the Church, an optical illusion.
We can urge them to pray a daily rosary because it is said that someday the scapular and rosary will save the world. Nothing was said that the Mass and Sacraments would save the world because Our Blessed Mother knew the Mass and Sacraments would be dumb downed to nothing. An abomination of desolation as foretold in the Bible.