A good bit
When someone talks about something like it’s the greatest thing ever, and then they fail at it completely. It’s like when they say it’s going to be a ‘good bit’ and it’s just a disaster.
‘I’m going to do a good bit’, he said, then fell off the stage
‘That’s a good bit’, she said, then spilled her drink
‘It’s going to be a good bit’, he said, then lost his voice