The full form of YBF is your best friend.
In most cases, “YBF” refers to “your best friend.”

A quick search for the acronym “YBF” reveals that there are several different meanings. Although it can be used in many ways, one seems to be the most widely accepted. It can be used in regular conversation or it can be used as a way to close a letter or message.

This word can be used by anybody in most situations. It is more likely to to be used by younger people that are probably female. If an older male were to use “YBF,” it may be in a joking manner. It can be used at work because it isn’t offensive, but it does make the user look more childish or not as professional.

Example 1:
Friend 1: I am so mad at Craig. How could he forget that we were going on our trip tomorrow?
Friend 2: What happened? I thought he was YBF.
Friend 1: He was my bf, but not anymore. He has been super flakey. I’m done.