Lick a friend
BFF is a Steam achievement.
Rarely, a goat NPC in Goat MMO Simulator will have the name of a friend on your Steam friends list. Lick them to earn the achievement.
The best way to see lots of goats to search for a friend is to walk between Goatwind and the goat/sheep battle in the Gold Fields. Every time you change maps the names will change, and both locations have a lot of goats present.
According to the source code[1] present in the Goat Simulator Development Kit, friends will only have the chance to show up if they are actively playing Goat Simulator at the time the fake MMO chat system is initialized. The chance that any given goat NPC has a friend's name is determined by a formula, as follows:
N = # of friends playing F = # of fake nicknames in the configuration files % Chance = (2π * N / (N + F)) * 100% Chance is capped at 100%.
The list of fake nicknames contains 232 names by default.[2]