A person who unnecessarily flaunts his knowledge in front of others. Or someone who likes to advise everyone even though nobody asked him to.
Rakesh: Sir, how do we do this problem.
Mukesh (interrupting): Oh, it is so easy, I did it yesterday. It uses basic trigonometry.
Rakesh(in his brain): Gyanchod, saala !!! (Fucking, gyanchod!!)
'Gyalchester' is the well-known nickname for the parish of Manchester, Jamaica, West Indies. "Man" is replaced by "Gyal" to note that there are very beautiful women in this area. This local term was popularized worldwide by Drake and OVO-UnRuly.