Prepare your Mentos bomb. You'll use about 7 mints and a long strip of masking tape. Line up the mints on the sticky side of the masking tape, but put them on their sides, just like they are inside the roll. Wrap the remaining length of the masking tape around the stack of Mentos, leaving the sides exposed. You can put on as many layers of tape as you want to ensure that it will hold, but it's important to leave it wide open on the sides.
Make a small loop of tape, so that it's sticky all around. Take the cap off of the Diet Coke bottle and wipe the inside dry if it is wet. Put the sticky tape loop inside the cap. Then stick one end of the taped-up mint stack onto the other side of the loop.
Put on your protective goggles and give appropriate instructions and warnings to others in the area, because things are going to move pretty quickly from here on out.
When you're ready, put the cap on the bottle, carefully guiding the mint stack through the opening. Once the mint stack is in, you have to do this super fast. Screw the cap on tight, then shake the bottle for about 8 seconds. Hold the bottle with both hands, with the cap pointing toward the ground. Then raise the bottle high above your head and use both hands to throw it cap-first at the ground as hard as you can.
Hopefully, you've avoided getting hit with the bottle so that you can observe it hurtling through the air. Now go find the bottle to throw it away, then go clean yourself up.