Can I apply for an e-visa while already in Thailand?

The only thing e-visa changed is the method of applying, switching from paper to online application. So your question is basically "has anyone applied for a visa at xxx embassy while already being in Thailand?" It's not allowed as you must apply at the Thai embassy where you are physically located.

One part of the application requires you to submit all stamps in your passport from the previous year, so if they see you are in Thailand they will reject your application.

Another part of the application is a plane ticket from the country where you are applying from to Thailand, which is another potential method of disqualification.