Common Sense
Do you feel holy when you are doing these things.
Do you think Jesus did this, would you feel comfortable telling Him you masturbate.
This seems to me to be common sense.
You think bad thoughts when you are doing this, this is not a holy practice.
Regardless if it makes you feel good.
This life is not about feeling good it is about winning lost souls.
As to some of the comments earlier about requiring scripture to tell you exactly about the question:
1 John Chapter 1
"God is light and in him there is no darkness at all."
Also anything that is not for God is against him, so tell me that masturbating is for God.
Although you may prove here that he did not specifically forbade it, he certainly did not condone it.
And I think you will have a much harder time proving that masturbating is for God.
Also, do not pick apart the words in this forum for your own good.
Know the motives of your heart, for God certainly does.
But it is ok, because all sin is forgiven, there is grace in God for all sins.
BUT JUSTIFICATION WILL NOT BE FOUND FOR THINGS OF DARKENESS!
Again in 1 John he says,"If we say we have not sinned we make Hima liar, and His word is not in us."
Thats what God has put on my heart.