scare so stiff meaning

[American slang]
Fig. to frighten someone severely. (Stiff = dead.)
  That loud noise scared me stiff.
  The robber jumped out and scared us stiff.

• scare someone stiff:    [American idiom]to ...
• scare so or sth away:    [American slang]to ...
• scare so or sth up:    [American slang]Ru ...