I once was at a Mars volta gig at the Astoria in london, and was using my bullet pipe (smokeless)

but an usher/steward saw me and got reli pissed off and said if i did again she'd kick me out , and literally didn't take her eyes off me for the entire gig. and i mean LITERALLY her eyes did not move from me ONCE, all 4 of us would ceck over every few mins and she'd be staring,
However in between me an her where about 30 people smoking joints.
Wasn't untill after the gig I realized what must have happened:She must have thought it was a crack pipe, It can look like one to someone who doesn't know better very easily,
And people smoking joints they can overlook because they can just dismiss them and "assume" they where cigarettes, takes the blame off their backs mostly, in a legal sense.

So now I always bring joints to gigs.

Jonny