I would only wear a blazer without a tie. If a tie is appropriate then it's time for me to wear a suit.I know that some may consider Blazers old fashioned now but for a lot of occasions I prefer Blazer and trousers to a suit.
For me shorts means no shirt.I had thrown out all my tailored shorts it would seem, so only denim left. Tend to wear short linen, light Oxford shirts. White spring courts are my favourite summer trainers.