As originally coined by Adam Carolla on the Loveline radio show then later in his podcast, "Brewing" is the act of pinching the head of your penis and starting your urine stream. Continue to hold the head closed while pressure builds up in the urethra (the brewing), then release the head to shoot urine with great force and distance. As Adam's stories go, he and his jack-off buddies used to go into the boys bathroom in high school and if there was someone in one of the stalls, they would go into the stall next to it, brew, then shoot their stream over the partition and land it on the unsuspecting victim.
Ray saw a freshman go into the stall, and as per usual brewing claimed another victim.