There are times when you just really don't want to talk, and Google knows this. It is the reason they build a call screening tool into the stock dialer. You can tell your phone to do one of three things when a call comes in including reject the call, prevent the number from being displayed on the call log, and even stop the dialer from showing a notification.
This can be used by third party apps like Truecaller to disregard known bad numbers. Somehow I end up receiving about 2-3 telemarketing calls per day. This tool may help to end that headache.
Via Android