Macro to concatenate unique combinations??

Thanks in advance for any help!

I have the following example values in Column A and I want to concatenate each unique combination to a list.

A
B
C
D

Example necessary output:

A vs. B
A vs. C
A vs. D
B vs. C
B vs. D
C vs. D

Notice there are no duplicates (e.g., A vs. B / B vs. A). I have found many macros that will create all the duplicates but none that will create only unique. Thanks again!!