My mouse keeps double clicking when I'm using the Pen Tool.

Hello @heavywulf,

We understand that encountering technical issues can be frustrating. As suggested by Monika, it could be possible that the switch on the mouse has failed and is leading to erratic clicks.

Would you mind checking if the mouse also behaves this way with other applications as well? If not, kindly try to reset Illustrator's preferences as described in this article (https://helpx.adobe.com/illustrator/kb/troubleshoot-preference-issues.html) and running Illustrator under a different user account and checking if it helps.
Disclaimer: Please note that resetting preferences will remove all custom settings, and Illustrator will launch with the defaults. You may save a backup of these settings from the location mentioned in the article.

If you don't mind, could you please follow the steps and share your observations with us? We appreciate your time and effort in helping us resolve this issue.

Looking forward to your response.

Thanks,

Anubhav

Do you have any possibility of using a different mouse?

They can get just broken. Hardware-side. That little clicking thing then is at the end of its life.

Does the mouse work in other design apps where you have to click a lot?

Is it just the pen tool in Illustrator? Or other tools as well - e.g. the liquify tools?

When was the last time you rebooted the computer?