Apple

Following/Bump

Make your default ringtone silence with no vibration. Add specific ring tones to those contacts you want to talk with. Let your voicemail sort out the calls to ignore or answer.

I usually just hit the volume down button.

Press the red button instead of the green one when someone rings, lol.

I just ignore it or hit the big red button on the screen.

Push the power button once to mute it and push it again to decline the call

It's not a double-click. Press once to stop the ringer, then press again to reject the call.