Here's what it means in practice:
* Someone who makes silly mistakes: Spilling their coffee, forgetting important dates, or getting lost in familiar places.
* Someone who doesn't understand simple things: Misinterpreting instructions, asking obvious questions, or failing to see the obvious solution.
* Someone who is awkward or clumsy: Tripping over their own feet, dropping things, or accidentally bumping into people.
* Someone who lacks common sense: Making decisions that seem illogical or unsafe.
Important Note: While "doofus" is usually meant to be a playful term, it's important to be mindful of the context. If you're using it to describe someone, make sure they wouldn't be offended.