Not think much of (someone or something) verb phrase
To have low respect or regard for someone or something; To evaluate someone or something with a negative attitude
Although you tell lies only once, people will not think much of you.
I admitted to John that I didn't think much of his new girlfriend.
The professor hasn't thought much of your project so far, so you'd better try a bit harder!
The examiner didn't think much of our new product due to the lack of creativity.
Used in response to a threat suggesting that the threat is a weak one.
To underestimate someone, something or oneself
1. To consider something as true, real or available without questioning it
2. To fail to show proper appreciation or gratitude to someone or something; to underestimate the value of someone or something
The verb "think" should be conjugated according to its tense.