Them: "Hey dude, can I use your computer real quick for a second."
You: "Err, hold on a second, I need to do something..."
Them: awkward silence
But more seriously it really depends on what appears in that search results and for which queries. If it's done properly it only triggers when there's a very relevant mail matching the query, which would be unlikely from just a casual search from a friend.
Also if just the title is shown, it doesn't reveal much.