I learned that the hard way years ago after eating a top porn star.
No way, no how, no more whether it's a star or a regular Joe.... The symptoms of illness from catching such "bugs", i.e. parasitic infections, are hideous and once is enough. A simple shower is not going to eliminate parasites that the other guy may have in his system.
If your friend refuses to use the smarts he should possess at some basic level or ask his medical professional about the risks of eating out, he has no one else to blame but himself.