THANK YOU, HEATHER, FOR A SOLUTION.
My kids love to take the straws in and out of lidded cups over and over, which can make a mess.
One day, I gave one boy juice in a cup with a lid and a crazy straw. For some reason, he wasn't crazy about the crazy straw, so I turned it upside-down. What I didn't realize until my husband pointed it out was that turning the crazy straw upside-down locked it into the cup! No more taking out the straw to play with it!
More: We've got lots of hacks involving straws.