I believe (but must ask at the airports I will soon pass through - expect differing answers) that it doesn't matter what the "sharp" is, so long as it is no more than 60mm long. On the other hand there is a rule that says "no tools" - its interpretation is pretty much entirely up to the person doing the search. A toothbrush, a comb, etc. is a tool, as I have pointed out at airports before - ah, but..... is the reaction. I tend to agree with Naomi - if your intention is to deny a determined person the opportunity of doing harm at an airport or on board an aircraft then surely you would not encourage everyone to have access to glass bottles. A lot of damage can be done in what is a mere instant. Why not plastic bottles, or forget the flammable liquid altogether......But think of the lost jobs, lost profits.... Tough, I would say.