Blithering (adjective)

Stupid and ineffectual.

Origin:

Mid 19th century: origin uncertain, possibly a blend of blather and witless.

Examples:

1. The blithering fool had no idea what he was doing, and managed to make a complete mess of things.
2. The blithering idiot seemed incapable of doing anything right, and was constantly getting into trouble.
3. The blithering fool couldn't seem to understand the simplest instructions, no matter how many times they were explained to him.
4. The blithering idiot was so clueless that he walked into a glass door, thinking it was open.
5. The blithering fool had a tendency to say the wrong thing at the wrong time, much to the annoyance of everyone around him.