There is a trend at most private clubs to relax a bit on the dress code issue - especially with denim.
If you want new young members, you had better pay attention. Clubs want revenue, not excuses from new members and guests why they seek food and beverage elsewhere.
The mock turtle...?...yea, you can wear it. But, as I said before, you may get heckled.
Plus, the pro will know you sure didnt buy it in his shop!!