Definition
Alternative form of all mouth and trousers.
Origins
A possible corruption of all mouth and trousers, but consistent with phrases of the form all hat and no cattle and all bark and no bite. The implication of this phrase is that the person boasts, but is a laughing stock.
How People Actually Use It
Someone who can talk a good game but cannot back himself up. Relies heavily on others who are his opposite (able, but a poor orator) to sort out any problems. One who makes idle threats.
"Random13yearold: I'll hax your computer! I'll hack a virus!!!111 KFJ: You're all mouth and no trousers, but I'd love to see you "hack a virus"."
Source: Urban Dictionary