What is the effect on my credit score if I borrow $100,000. and repay it in 4 months?

It really depends on several variables in my opinion, such as your current credit score and your previous credit line limits. Zero to hero throws up a red flag sometimes. Also, do you have "any" late payments showing on your accounts? What you write of is practiced by some to attempt to achieve what your friend did. Some do, while it can have an adverse effect others. This is just an opinion, but I liken a credit score shooting through the rough to "getting rick quick." There are hidden risks to both. You sound like a wise, well educated person asking this question. Great question.

For the younger readers, to build really good credit consider a less dramatic, more steady pace. Your credit lines aren't in this level now anyhow. Try to give these informational articles a read to learn more...