I am new to android and just by going into Google Play I can see every app my friends downloaded. I am really feeling uncomfortable about this since I don't like to feel exposed.
Does anyone knows how to block this "feature"?
I don't think that there is any trick available which you can use to hide the apps downloaded from your friends until or unless you unfriend your friends over your G+ account.
But I have got another trick for you which is going to work for you like whenever you download app, try getting the .apk file downloaded from third party sites say I want to download whatsapp and don't want my friends to see. I will download whatsapp.apk file directly from the Whatsapp website and then I can install the apk file independently and my friends will never know that I have downloaded whatsapp, just make sure you don't get the apps from PlayStore and it will not be shown!