A Burp Is Spontaneous. A Burp Is Not Romantic.

A friend asked the other day, "What makes something romantic?" and I thought it would be a good question to play with here. Are there necessary and sufficient conditions? Is it purely subjective? There are certain things that will make almost anyone go "Oh, that was sooooo romantic," meaning that it doesn't simply seem to be a matter of taste. What characteristics of an act will tend to make it romantic?