There are a number of difficult passages in Psalm 141, but, in this 
post, I want to concentrate on v 5.  In the KJV, the verse reads: “Let 
the righteous smite me; it shall be a kindness: and let him reprove me; it shall be an excellent oil, which shall not break my head: for yet my prayer also shall be in their calamities.”
“Let the righteous smite me.”  In the Hebrew, the word translated as 
“the righteous” is in the singular, and so there is one interpretation 
that says that the righteous one in Psalm 141:5 is God: that the 
Psalmist is receptive to God’s discipline and chastising of him.  
Keil-Delitzsch refer to scholars who think this, but I’d like to quote 
Jimmy Swaggart’s words in his study Bible: “‘The Righteous’ could only 
refer to the Heavenly Father.  God does not allow fellow Christians to 
smite each other.  Vengeance belongs to Him, and no one else.  It is 
proper for the Lord to chastise us, but not proper for anyone else to do
 so…”
I don’t think that Psalm 141:5 means what Swaggart says it means.  As
 Keil-Delitzsch note, “righteous” is not used as a “direct appellation” 
for God in the Hebrew Bible, which means that God is not called “the 
righteous one” in the Hebrew Bible.  God is said to be righteous, but he
 is not called “the righteous one.”   (UPDATE: An exception may be Proverbs 21:12, which seems to concern God's punishment of the wicked.)  Often in the Book of Psalms, when 
we see the term “the righteous” in the singular, it refers to the 
righteous human being.  The message of Psalm 141:5 is probably that the 
Psalmist welcomes rebuke from righteous human beings, and we see that 
sort of theme elsewhere in the Hebrew Bible (John MacArthur cites 
Proverbs 9:8; 19:25; 27:6; 27:17).
But I can understand why Swaggart might have preferred for the 
righteous one of Psalm 141:5 to be God rather than God’s people.  God’s 
people—-or those who call themselves such—-can be pretty nasty.  
Swaggart probably felt that he had experienced this during his own 
scandals.  Whereas God’s people can put a person down without compassion
 or knowledge of all of the facts, God can be trusted to be a perfect 
disciplinarian because God is compassionate, knows the whole story, and 
is aware of what people need at particular stages in their journey.
But can God use rebuke from a righteous person?  I don’t rule
 that out; I just have a hard time putting a great deal of stock in the 
times that Christians have rebuked me, for I have felt that their 
rebukes have come from judgmentalism, narrow-mindedness, and incomplete 
knowledge of me and what I was going through.  That’s not to say that I 
found their rebukes to be totally off-base, for I can learn 
about how I am coming across from hearing people’s impressions.  But I 
have a hard time equating their judgments with God’s opinion, for I’d 
like to believe that God is more compassionate and fair than they are.
I should note that the Psalmist values rebuke from the righteous—-from
 those who do right.  Because humility is a virtue, one would hope that 
rebuke from a righteous person would correspond with genuine love and 
humility, rather than being a mere put-down that allows the person 
rebuking to feel superior.  I doubt that there is a whole lot of love 
and humility when Christians rebuke people they barely know on Facebook 
or in blogs.