Bosch Beer is a long-running FS2 meme. Veteran HLP member Max Sterling created it and popularized it with a clever page on the Robotechlan site: http://www.robotechlan.com/freespace2/bosch/
In Max Sterling's own words1:
Bosch Beer arose out of the general silliness that was taking place on the forums at the time. Many people with various photoshop skills were creating logos mixed with FS2 jokes, "memes" before the word really was used as an internet term. One day I noticed the similarity between Captain Bosch's name and Busch beer -- it was a simple matter to photoshop the "U" into an "O." Slightly changing the beer's catchphrase to "Head for the Shivans" one of the more enduring FS2 memes was born.
The date of creation was "probably like 2000 or 2001"2.
1 Via PM to Goober5000, 5/19/2014
2 Via PM to Goober5000, 1/29/2015