\begin{tabular}{|l|ccc|}
\hline
\diagbox{Time}{Room}{Day} & Mon & Tue & Wed \\
\hline
Morning
& used & used &
\\
Afternoon &
& used & used \\
\hline
\end{tabular}
代码如下：
\begin{tabular}{|@{}l|c|c|r@{}|}
\hline
\diagbox[width=5em,trim=l]{Time}{Day} & Mon & Tue & Wed\\
\hline
Morning
& used & used & used\\
\hline
Afternoon &
& used & \diagbox[dir=SW,height=2em,trim=r]{A}{B} \\
\hline
\end{tabular}
具体使用和参数参看：
http://ctan.org/tex-archive/macros/latex/contrib/diagbox
