Strike-through Tilde Accent

A variation on my answer at Big tilde in math mode, showing \reallywidetile and \reallywidenotilde.

\documentclass{article}
\usepackage{scalerel}
\usepackage{stackengine,wasysym}

\newcommand\reallywidetilde[1]{\reallywideXtilde{#1}{\AC}}

\newcommand\reallywidenotilde[1]{\reallywideXtilde{#1}{\NAC}}

\newcommand\NAC{\stackengine{1.5\LMpt}{$\SavedStyle\AC$}{\smash{$\SavedStyle\vstretch{.35}{/}$}}{O}{c}{F}{F}{L}}

\newcommand\reallywideXtilde[2]{\ThisStyle{%
  \setbox0=\hbox{$\SavedStyle#1$}%
  \stackengine{-.1\LMpt}{$\SavedStyle#1$}{\kern.3ex%
    \stretchto{\scaleto{\SavedStyle\mkern.2mu#2}{.5150\wd0}}{.6\ht0}%
  }{O}{c}{F}{T}{S}%
}}


\def\test#1{$%
  \reallywidetilde{#1}\,
  \scriptstyle\reallywidetilde{#1}\,
  \scriptscriptstyle\reallywidetilde{#1}\qquad
  \textstyle\reallywidenotilde{#1}\,
  \scriptstyle\reallywidenotilde{#1}\,
  \scriptscriptstyle\reallywidenotilde{#1}
$\par}

\parskip 1ex
\begin{document}

\test{abcdefghijklm}
\test{abcdefghijk}
\test{abcdefghi}
\test{abcdefg}
\test{abcde}
\test{abc}
\test{ab}
\test{a}
\test{f}
\test{A}
\end{document}

What about this?

\documentclass{article}
\usepackage{amsmath,amssymb}
\def\nottilde#1{\overset{\ifx#1f\hspace{.5ex}\fi\lower0.8ex\hbox{\tiny$\nsim$}}{#1}}
\def\xtilde#1{\overset{\ifx#1f\hspace{.5ex}\fi\lower0.8ex\hbox{\tiny$\sim$}}{#1}}
\begin{document}
$\tilde{e}\xtilde{e}\nottilde{e}\xtilde{f}\nottilde{f}$
\end{document}