make a phone call to John Wayne
This is a more inside way of saying you have to drop a deuce (take a crap), it works really well in an office setting so that you may let your close, personal co-workers know where you are going without letting everyone else know. This is derived from
John Wayne's nickname being "The Duke", and can be shortened by simply saying "I have to
make a phone call", or added to by saying "man
John Wayne has been calling me all day."