A spider's favorite thing to do on a computer is... WEB-surfing! 🕷️🖥️🏄♂️
Explanation: Spiders are known for creating intricate webs, so it's only natural that their favorite activity on a computer would be web-surfing! It's a pun that combines the spider's affinity for webs with the common term "web-surfing" which refers to browsing the internet. 🕸️😄