Sombrero (cocktail)

A “Sombrero” cocktail is Kahlua (the Mexican coffee liqueur) and cream or milk. The drink is first cited in the 1970s. It is unknown why the name “Sombrero” (a Mexican hat) was chosen for the Mexican drink, but it’s a logical enough choice for a popular tourist drink.
   
A 1976 Dallas Morning News article (below) states that Dallas resident Curtis Bryan invented the “Sombrero,” but this hasn’t been confirmed with any other evidence.
     
       
Kahlua Cocktails
Sombrero
Ingredients: 1 Part Kahlua, 2 or 3 Parts Cream or Milk
Method: Pour the Kahlua and Cream or full cream milk into a short glass (ice optional) and stir.
     
About.com: Cocktails
Sombrero
From The Bartender’s Black Book
 
INGREDIENTS:
2 oz Kahlua or coffee brandy
milk or cream
PREPARATION:
Pour the Kahlua or coffee brandy into an ice-filled old-fashioned glass.
Fill with cream or milk.
   
18 November 1973, Fort Pierce (FL) News Tribune, pg. 18, col. 1 ad:
Mr. Boston Sombrero Cocktail Fifth 2.99  
(Foremost Liquor Stores—ed.)   
   
24 January 1975, Pocono Record (Stroudsburg, PA), pg. 18, col. 7:
Although many people would disagree, Mrs. Hopkins, the Vasalboro, Maine, goat owner, says the taste and consistency of goat’s milk are extremely close to cow’s milk. She says she proved her point to friends by mixing goat’s milk with Kahlua to make a sombrero cocktail, and no one could taste a difference. 
 
Time magazine
Cows with a Kick
Monday, Apr. 19, 1976  
During Prohibition, indiscriminate tipplers discovered that whisky could be downed with impunity in public places if it were concealed in a glass of milk. A few learned to like it that way and kept the habit after repeal, continuing to order an occasional brandy alexander (cream, brandy and creme de cacao) or a sombrero (milk and Kahlua).
 
13 June 1976, Dallas (TX) Morning News, section A, pg. 42:
Curtis Bryan, an instructor at the Dallas academy (Texas Academy of Bartending—ed.), says a drink he invented, called the sombrero (Kahlua and creme), has become the No. 1 drink in Boston “of all places.”
 
Google Books
The Quintessential Dictionary
by I. Moyer Hunsberger
New York, NY: Hart Publishing Company, Inc.
1978
Pg. 211:
...continuing to order an occasional brandy alexander (cream, brandy, and crème de cacao) or a sombrero (milk and Kahlua).