A “sipster” (sip + -ster, hipster) is someone who sips. An 1896 dictionary of slang included “sipster” with other term describing someone who is drunk; a 1995 slang dictionary defined “sipster” as “a tippler, a drunkard.”
 
However, a “sipster” need not include only those who drink alcoholic beverages. A 2009 newspaper photo caption described a “Seattle coffee sipster.” A 2005 newspaper story mentioned “pupu-platter-loving hipsters and sipsters.” A modern “sipster” is not a drunk, but a coffee-drinking (or wine-drinking) hipster. The Simon Sips coffeehouse in Manhattan calls its loyal customers “sipsters,” according to a February 2013 article in the New York (NY) Times,

“Sipster” is also a trademarked name (since 2003) for children’s drinking and training cups.
 
 
Google Books
Slang and Its Analogues, Past and Present:
Volume 4
By John Stephen Farmer and William Ernest Henley
Printed for subscribers only
1896
Pg. 257:
Lushington.
... sipster ...
 
Google Books
Slang American Style:
More than 10,000 Ways to Talk the Talk
By Richard A. Spears
Lincolnwood, IL: National Textbook Co.
1995
Pg. 350:
sipster n. a tippler, a drunkard.
 
Seattle (WA) Times
Friday, May 21, 1999 - Page updated at 12:00 AM
Budget Bites
(...)
Caffe Infinito Italian cafe. Not content to offer shoppers just another gussied-up coffee joint with fancy pastries, owner J.D. Hemmat presents microbrews and wines-by-the-glass and weekday happy hours for bargain-hunting sipsters at his Italian-style Redmond Town Center cafe.
   
Seattle (WA) Times
Wednesday, July 13, 2005 - Page updated at 12:00 AM
Taste of the Town
What’s new? Bastille Day celebrations, a third Malay Satay Hut and more
By Nancy Leson
(...)
Those pupu-platter-loving hipsters and sipsters should be pleased to note that Luau’s original owners, Thomas and Jessica Price, have regained ownership of the restaurant and bar, sold last year
   
The Spokesman-Review (Spokane, WA)
January 11, 2009 in City
Robert Silva, a Seattle coffee sipster, gets a noseful at Stumptown Coffee Roasters on Capitol Hill in Seattle.
   
Seattle (WA) Times
April 6, 2009 11:01 AM
Flower power: bartenders pick St-Germain
Posted by Nancy Leson
If you hang out in bars (which I do, but only if there’s great food involved), perhaps you’ve sipped a cocktail made with St-Germain:
(Photo—ed.)
Sophisticated sipsters worldwide have been impressed by this lovely liqueur.
 
Urban Dictionary
sipsters
the act of taking a sip of an alcoholic/ non-alcoholic beverage
by bwuv Jul 17, 2009
   
New York (NY) Times
Published: February 9, 2013
Java Jive
By Ben Schott
SIMON SIPS
NEW YORK CITY
SIPSTERS: Local customers. (Also, hipsters who insist on porcelain rather than to-go cups.)
 
(Trademark)
Word Mark SIPSTER
Goods and Services IC 021. US 002 013 023 029 030 033 040 050. G & S: Children’s drinking and training cups. FIRST USE: 20031000. FIRST USE IN COMMERCE: 20031000
Mark Drawing Code (1) TYPED DRAWING
Serial Number 78226638
Filing Date March 17, 2003
Current Basis 1A
Original Filing Basis 1B
Published for Opposition November 11, 2003
Registration Number 2907280
Registration Date November 30, 2004
Owner (REGISTRANT) Playtex Products, Inc. CORPORATION DELAWARE 300 Nyala Farms Road Westport CONNECTICUT 06880
(LAST LISTED OWNER) PLAYTEX PRODUCTS, LLC LIMITED LIABILITY COMPANY DELAWARE 6 RESEARCH DRIVE SHELTON CONNECTICUT 06484
Assignment Recorded ASSIGNMENT RECORDED
Type of Mark TRADEMARK
Register PRINCIPAL
Affidavit Text SECT 15. SECT 8 (6-YR).
Live/Dead Indicator LIVE