\documentclass{article}
\usepackage{tikz}
\usepackage{pgf}
\usetikzlibrary{arrows, decorations.pathmorphing, backgrounds, positioning,fit,petri}
\usetikzlibrary{calc}

\begin{document}
\begin{tikzpicture}
\draw plot [smooth cycle, samples=10,domain={1:8},tension=1.5] (\x*360/8+5*rnd:0.5cm+1cm*rnd);
\end{tikzpicture}
\end{document}