The apéritif is typically a drink served before a meal, ostensibly to aid in digestion, though to what extent this is really the case is dubious at best. Any handy excuse invented for the imbibing of alcoholic beverages must be viewed with a skeptical eye. But no excuse is really needed to appreciate a good concoction; it's a pleasure in itself, not in need of any artificial encouragements or pretexts.
Here's one that I thought of. The imagination plays a big part in the invention of any kind of taste. The greater your familiarity with how flavors are experienced, the greater the possibility that you may divine the right consummation of spice and mouthfeel. Curiosity also plays a part.
Sweet vermouth is commonly drunk all by itself as an apéritif, but as a basis for mixing, it has just as much possibility as ordinary spirit goods (like bourbon or scotch). And its inferior strength means it should carry less of a kick, and hence fulfill the notion of apéritif, instead of a regular cocktail.
2 parts Carpano Antica Formula Vermouth
1/4 part St. George Absinthe Verte
1/3 part Becherovka liqueur
1/2 part fresh lemon juice
slice lcmon garnish
served on the rocks (stirred slightly)
This one won't chase the ladies away, either, which is always a consideration.