leave (one) flat
1. To leave one feeling bored, unamused, or unimpressed. His stupid puns left the entire audience flat. The characters were interesting, but the lackluster story really left me flat.
2. To abandon or forsake one, especially suddenly or unexpectedly. The manager just quit one day and left us flat. The office has been in total disarray since then. I thought the date had been going well, but she left me flat after we finished dinner.
3. To leave one alone or in a desperate situation with no money or resources. It will leave us completely flat if they don't approve our funding for next year. That electricity bill has left me flat until I get paid this Thursday.
leave someone flat
1. Fig. to fail to entertain or stimulate someone. Your joke left me flat. We listened carefully to his lecture, but it left us flat.
2. Fig. to leave someone without any money—flat broke. Paying all my bills left me flat. The robber took all my money and left me flat.
3. Fig. to leave someone completely and suddently alone. I was at the dance with Harry, but when he met Alice, he left me flat. They just walked off and left us flat.
Forsake or abandon completely, especially without warning. For example, He didn't tell her he wasn't picking her up; he just left her flat. [Colloquial; c. 1900] Also see high and dry; leave in the lurch.