be as keen as mustard
To be very enthusiastic about something. Primarily heard in UK, Australia. These new kids are as keen as mustard to be in the choir, so we can definitely get them to clean up the choir room for us. I know you kids aren't exactly keen as mustard to clean out the garage, but it really needs to be done. I hate having to study every night, but I am keen as mustard to get these exams over with.
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