This is not a fool-proof puzzle. You have to put your faith in an untested paper straw. I recommend that you only do this trick over a soft surface so that there is no damage if it doesn't work.

Show your friends an empty bottle and a paper straw. Stand the bottle on the table and then ask if anyone can lift the bottle from the table without touching it with anything except the straw. And it is against your rules (well, this is your puzzle!) to tie the poor defenseless straw round the neck of the bottle.

A few over-confident people may try, then you show them that it is really easy. Well, it is really easy indeed! 

You just bend the bottom couple of inches of the straw at a sharp upward angle to create a sort of hook.

Now you can push the bent end of the straw into the bottle and when the bent piece lodges inside the bottle, you can easily lift it off the table.