some singular nouns ends with 's' such as trousers, glasses,.... I have heard and read the phrase 'a trousers' and here is a qoute from a site as well:
"For a very simple evening, even between buddies (like evenings of clubs...) skirt and top will make the deal : choose a moulding skirt and top. You can choose a moulding trousers and top too if you feel better with a trousers."
but is it common between english speakers to use this phrase (a trousers - a glasses)??