When you're on the spot and you're looking to say some concrete shit but you have nothing to say.
Donald Rumsfeld explained to the committee where the WMD's were, but he was clearly grasping at straws.
Making wild and often times unbelievable assumptions or using far fetched ideas and possibilities to reach the desired conclusion.
The police were trying to make a conviction, but they were just grasping at straws.
to have false ideas or beliefs about something.
Larry thought Sue loved him, but he was just grasping at straws when he went after her.
(v.) giving someone the ol' reach around
; pulling at pubic hair during intercourse
He especially liked grasping at straws.