You're logged in to a remote host via ssh, about to su or whatever and just as you begin typing your super secure, character set conscious password you get:
Password: ~v [LogLevel DEBUG] su: Authentication failed
You have just tripped an SSH escape sequence. From man ssh:

ESCAPE CHARACTERS
 When a pseudo-terminal has been requested, ssh supports a number of
 functions through the use of an escape character.

 A single tilde character can be sent as ~~ or by following the tilde by a
 character other than those described below.  The escape character must
 always follow a newline to be interpreted as special.  The escape
 character can be changed in configuration files using the EscapeChar
 configuration directive or on the command line by the -e option.

 The supported escapes (assuming the default ‘~’) are:
 ...

 ~V      Decrease the verbosity (LogLevel) when errors are being written
         to stderr.

 ~v      Increase the verbosity (LogLevel) when errors are being written
         to stderr.

The solution is simple: either choose a password that doesn't begin with an escape sequence or enter a double tilde: ~~