Many humorous answers.
My experience from my trip last year in Europe, including a week long tour with (rented) bikes in Holland/Belgium.
I was carrying my bike repair tool bag (weighs a bit) in the carry-on, in case our luggage got lost and to lighten up our normal suitcase. Boarding the plane from Zurich to Hanover (prior to our tour) the safety screener removed and confiscated my needle nose pliers 'because they could be used as a stabbing weapon' (making a characteristic motion). The fact that they were selling Swiss Army knifes at the duty free didn't sway him... You don't want to get into an argument with these guys, so I waved goodbye to my 20 year old pliers and moved on.
A Brooks saddle mounted on a seatpost could be considered a tomahawk...