She can't lift anything heavy, so she's a fat lot of use!'I'm going to tell him exactly what I think of him.' 'A fat lot of good that'll do you!'
a fat lot of good
Something that is useless or not worth the effort. A fat lot of good that did me, spending all that time carefully wrapping the ceramic mugs only to drop the box on the floor and break them all.
a ˈfat lot of good/help/use
(spoken) not at all good/helpful/useful: A fat lot of use that would be! What a stupid idea.He was a fat lot of help, I must say!