paper tiger 
noun
A person or thing that appears threatening but is ineffectual.In the event, it turns out that the SEC has imposed no sanction of any material consequence, and is in danger of becoming a paper tiger under new chairman, Harvey Pitt....
- A general thrust of my argument is that the postmodern turn in anthropology threatens to be a paper tiger.
- All this activity generated little pressure on legislators, making Schwarzenegger look like a possible paper tiger, very popular with the public but not able to generate much pressure to move legislative votes.