I pretty much hear some friend in the negative sense as in
Some friend you are!
How can some friend be used to express approval?
Please, provide examples and you may want to find out how you could help put some light on normal and sarcastic situations. The problem is that tone and context may play a significant role in catching on to the meaning.
Merriam Webster's Advanced Learner's Dictionary
a - used to express approval
- That was some game! [=that was a very good/enjoyable game]
b - used to express disapproval, disappointment, etc.
- You have some nerve [=a lot of nerve] to say that!
- You don't know how to get there? Some navigator you are! [=you're not a good navigator]
- Some friend he is—he left me stranded at the train depot.