Great question! I hadn’t seen it in the other topic!
Some crystals are piezoelectric, which means that wheen squeezed or compressed, they produce an electrical charge that we can tap into. That is why they are used in medical devices and computers. They have a memory and give off a pulse or a charge.
If you are using them for healing or have spent some time programming them for a specific intention, it’s best not to let others touch them.
However, some people love to share their crystals and why not? They are an amazing subject of conversation and a lovely gift. 
If a crystal feels or looks differently after a person held it, it could be that the person had bad energy/intentions, OR it may be that you just don’t like that person and you have unconsciously attached negative energy to them. Sometimes our own judgments can cloud our perception.
If that happens, you can cleanse it afterwards (spray sage, smoke it with incense, leave it on a piece of Selenite for a few hours, etc).
The best approach is to follow your intuition. Maybe have some crystals out in plain sight, that are meant to be touched and enjoyed by others. Then there are others that are strictly for your own use.