Step 1: Right click on the game in your library
Step 2: Scroll down until you see "Delete game Content"
Step 3: Press the left mouse button

BOOM! You have sucsessfully played Worm.is, but there is more!

Step 4: Spam miniclip that someone has copied them
Step 5: Write a nasty review of the game

and there you go! You have played worm.is!