In the Suez Canal? A lot!
Have you ever heard that a terrorist attack occurred in the Suez Canal? Although it's narrow enough that targeting any vessel will block it completely and allow for more time "and chaos" to target other "suspected" vessels.
Like what? Because it hasn't happened yet doesn't mean it isn't a vulnerable target. Most of the planning - acquiring the explosives, getting them into the canal zone, arranging a small boat, finding willing martyrs, etc. - are things that would be done well ahead of time and have nothing to do with whether a ship displays a banner or not.