How to include a Lenny face in a LaTeX document? e.g. ( ͡° ͜ʖ ͡°)

Staightforward with a stack.

\documentclass{article}
\usepackage{stackengine,graphicx,trimclip,scalerel}
\begin{document}
\savestack\eye{\rotatebox{90}{$^\circ\mkern-6mu\raisebox{1pt}{)}$}}
\savestack\nose{\raisebox{3pt}{\scalebox{1}[-1]{\clipbox{0pt 1pt 0pt 0pt}{?}}}}
\savestack\mouth{\rotatebox{90}{(}}
\scaleleftright{(}{\stackanchor[2pt]{\eye \nose \eye}{\mouth}}{)}
\end{document}

From there to a macro follows directly:

\documentclass{article}
\usepackage{stackengine,graphicx,trimclip,scalerel}
\savestack\eye{\rotatebox{90}{$^\circ\mkern-6mu\raisebox{1pt}{)}$}}
\savestack\nose{\raisebox{3pt}{\scalebox{1}[-1]{\clipbox{0pt 1pt 0pt 0pt}{?}}}}
\savestack\mouth{\rotatebox{90}{(}}
\newcommand\Lenny{\scaleleftright{(}{\stackanchor[2pt]{\eye \nose \eye}{\mouth}}{)}}
\begin{document}
This is my Lenny face: \Lenny
\end{document}

And here is a variant that won't distort line spacing:

\documentclass{article}
\usepackage[nopar]{lipsum}
\usepackage{stackengine,graphicx,trimclip,scalerel}
\savestack\eye{\rotatebox{90}{$^\circ\mkern-6mu\raisebox{1pt}{)}$}}
\savestack\nose{\raisebox{3pt}{\scalebox{1}[-1]{\clipbox{0pt 1pt 0pt 0pt}{?}}}}
\savestack\mouth{\rotatebox{90}{(}}
\newcommand\Lenny{(\scalerel{\stackanchor[2pt]{\eye \nose \eye}{\mouth}}{)}}
\begin{document}
\lipsum[2] \Lenny{} \lipsum[3]
\end{document}

---

Finally, a more proportioned variation, that can present Lenny from different font families (by way of optional argument):

\documentclass{article}
\usepackage[nopar]{lipsum}
\usepackage{stackengine,graphicx,trimclip,scalerel}
\newcommand\Lenny[1][]{\bgroup#1%
  \savestack\eye{\rotatebox{90}{\footnotesize$^\circ\mkern-6mu\raisebox{1pt}{)}$}}%
  \savestack\nose{\raisebox{4pt}{\scalebox{1}[-1.3]{\clipbox{0pt 1.5pt 0pt 0pt}{?}}}}%
  \savestack\mouth{\rotatebox{90}{(}}%
  (\kern-1pt\scalerel{\stackanchor[1.0pt]{$\eye\nose\!\eye$}{\mouth}}{\kern-1pt)}%
  \egroup%
}
\begin{document}
{\tiny rmfamily sffamily mirrored-ttfamily}\par
\Lenny\quad
\Lenny[\sffamily]\quad
\scalebox{-1}[1]{\Lenny[\ttfamily]}
\end{document}

If you use a Unicode aware TeX dialect like XeLaTeX it is just to paste the text and make sure the chosen font contains the characters.

\documentclass{article}
\usepackage{fontspec}
\setmainfont{DejaVu Sans}

\begin{document}
  ( ͡° ͜ʖ ͡°)
\end{document}

With some help from Detexify, I got this first approximation:

\documentclass{article}
\usepackage{tipa}
\usepackage{amsmath}

\begin{document}
    $\overset\frown{\smash(^\circ} \underset\smile{\ \text\textinvglotstop} \overset\frown{\ ^\circ} )$
\end{document}