Also known as 'BBF'; a friend whom you have very little in common with and you act on your best-behavior when you're with.
A best-behavior friend does not typically know the extent of your true character or transgressions because you misrepresent the truth to make yourself look good or innocent. A person with a best-behavior friendship may see the friendship as important or long-standing and so lying about situations or leaving out key facts becomes common.
After a night of dancing, Meg found herself secretly having drunk sex with her best friend's ex-boyfriend. Meg went for lunch the next day with her best-behavior friend Rachel and when Meg recounted her night to Rachel, the sexual elements were removed.
When working at a large organization with many divisions or departments, it may be necessary to differentiate between the extent of your working relationship with people in your organization. Co-workers would be those who work in your workgroup or department, or those whom you have a close working relationship with in another workgroup or department. Workplace acquaintances are people you know of but don't have a close working relationship with. These individuals are typically in other departments or divisions of the company.
In office fraternization situations, workplace acquaintances can be considered (although weakly so) the exception to the "I don't date co-workers" rule. The argument being that because he or she is not considered a co-worker (defined in the preceding paragraph), that person can be considered dating material because, even though you both work in the same company, you both work in a different division or department.
Rob: I am thinking of asking Trish from Accounting out to dinner and a movie.
Jon: Cool, she's hot! But you said you don't date co-workers.
Rob: She's in a different department, so that doesn't make her a co-worker, just a workplace acquaintance.