Seeing that many glory after the flesh, I will glory also.
Many - including the 'false teachers.'
After the flesh - as fleshly men boast; namely, of external advantages, their birth, doings, etc. (cf. 2 Corinthians 11:22), contrasted with "after the Lord" (2 Corinthians 11:17).
I will glory also - i:e., I also will boast of fleshly advantages, to show you that even in these I am not their inferiors, and therefore ought not to be supplanted by them in your esteem: though these are not what I desire to glory in (2 Corinthians 10:17).