My son (2.5) liked to do this too! I tried making him clean up his own messes, but he enjoys that even more! It became obvious that he was doing it because he got A LOT of attention for it. Nothing made me run faster than him making a big mess out of his drink. Timeouts didn't work for me either, but him not allowed to have a cup sure did. If he would spill I would take his cup away, explain why he got it taken away and then that was it. He would be really upset, but I persevered. Then I would let him have a "supervised" drink where I would give him his cup so he could take a drink and then take it back out of reach. Now he knows if he makes a mess (with any of his table food or drinks) he gets them taken away. Obviously if he accidentially spilled it, we would clean it up together and there would be no punishment. I hope that helps.