When washing rhinestone-embellished shirts, simply turn them inside out and wash in COLD water.
The rhinestones should not come loose in your washing machine, up to 165 degrees F. Simply turn the shirt inside out for washing and drying, if you remember. If you forget, don't worry, the shirt will probably be just fine!
As with all t-shirts that are 100% cotton, shrinkage can occur if left in the dryer too long. Try to avoid over drying your rhinestone tee, or better yet, let it air dry flat or on a hanger.