I've been taught that glasses (as in spectacles i.e. visual aid) are plural. It's also confirmed by numerous hits on the google (reference 1, reference 2, reference 3). In case the multiplicity of the equipment needs to be explicitly emphasized, one can say five pairs of glasses or simply reformulate in an appropriate way.
However, in the movie Come As You Are (about 45'15" in), the following dialogue takes place.
A: I lost my glasses.
B: It's right here. It's right here.
A: I lost my fucking glasses!
B: It's around your neck.
All the characters are native English speakers and there's no reason to make a grammatical error in the plot. The movie is subtitled so it can't be my hearing impediment. I even checked with two alternative sources for subs, all with consistent result.
Naturally, I expected they're right here and they're around your neck. What's up with that?