documentclass[10pt,a5paper,twoside]{memoir}

usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}

usepackage[brazil]{babel}
usepackage[showframe,pass]{geometry}

usepackage{comment}

makeatletter

% newenvironment{myenvironment}{comment}{endcomment}

letmyenvironmentcomment
letendmyenvironmentendcomment

makeatother

begin{document}

    This is normal text.

begin{myenvironment}

         How to make this environment be bfseries{verbatim}?

end{myenvironment}

end{document}

Excluding 'comment' comment.)
Runaway argument?
! File ended while scanning use of next.
<inserted text>
                par
<*> ./test2.tex

I suspect you have forgotten a `}', causing me
to read past where you wanted me to stop.
I'll try to recover; but if the error is serious,
you'd better type `E' or `X' now and fix your file.

! Emergency stop.
<*> ./test2.tex