\documentclass{article}
\newif\ifinfootnote
\let\realinsert\insert \def\insert{\afterassignment\infootnotetrue\realinsert}
\def\zz{\ifinfootnote FOOTNOTE\else not footnote\fi}%
\usepackage{color}
\begin{document}
\section{aaa \zz}
aaaa \zz \footnote{bbb \begin{bfseries}\zz\end{bfseries} and \zz}
\end{document}