Grandpa's old cough syrup usually refers to a hot toddy. A drink made with one shot of whiskey, a half cup of boiling water, a spoonful of honey, and a splash of lemon juice. Variations include adding cloves and/or cinnamon sticks then letting the drink brew for approximately 5 minutes before serving.
The nickname of Grandpa's old cough syrup comes from the hot toddy being used as a cold/flu remedy.
You guys been doing a little bit of boozing? Sucking back on grandpa's old cough syrup?
1. A plan to completely scrap a project after making significant progress and start over from scratch. Some parts of the original plan may be salvageable but most well have to be completely reworked for the new longhorn plan.
2. A reference to the scrapping of Windows Longhorn after three and a half years of development.
Guy 1: Hey you know that project you've been working on since you started with the company?
Guy 2: Uhhh, Yeah...
Guy 1: None of it's working and the business requirements have changed.