1. Fill half a drinking or wine glass with sparkling moscato (I like Bartenura). Add a few splashes of grapefruit juice and garnish the rim with a chunk of ripe grapefruit. 

2. Repeat as needed for each intrigued guest. 

Or, fill a glass pitcher halfway with the moscato. Add grapefruit juice, but leave a bit of room at the top. There should be a bit more moscato than juice. 

Tastes great over ice too!