I'm looking for an offensive single-noun term for "indecisive person," preferably short and cutting. Something along the lines of "nitwit" for "foolish person"; but now instead of "foolish," try "indecisive." No adjective synonyms, please.
Depending on context, you could use "a fence-sitter"
- fence-sitting - "a state of indecision or neutrality with respect to conflicting positions"
or "vacillating" (one who vacillates)
- vacillate - implies prolonged hesitation from inability to reach a firm decision. He vacillated until events were out of control.
or "a shilly–shally person"
- shilly–shally - (adj) irresolute, vacillating
In the US, if you called the person a "waffler", you'd probably be understood.
A ditherer. This has been suggested in the comments, and is the right word.
The term wuss is somewhat broader
A weak or ineffectual person (often used as a general term of abuse).
Oxford Dictionaries Online
But it is often used to describe somewhat who is fearful to commit or take action.
Procrastinator is a term that springs to mind. Useful to describe a person that is too busy concerning themselves with the pros and cons of a solution than actually implementing it