a mildly derogatory slang used to refer to Bangladeshi-Britons, especially those Bangladeshi-Britons of Sylheti descent. They speak Bengali horribly with thick Sylheti accents and those born and brought up in the U.K. usually speak English as well with a very thick accent. Their English dialect depends on the region of U.K. they are brought up in. All Londoni families own a restaurant which serve Indian cuisine and is a hub for providing jobs to their newly-arrived relatives from Sylhet who have decided to stay back illegaly.
These people try to give an impression of being really rich and well off to their Bangladeshi friends and relatives and think they are really of a higher class with more status and cooler than them just because they live in England, when in reality they are a bunch of jokes who neither the British nor the Bangladeshis really give a shit about. They have horrible sense of style and have no clue what big idiots other people think they are.
Note: This in no way applies to Bangladeshis living in other countries like the United States or Canada where the Bangladeshis living are actually sophisticated and educated unlike their British counterparts.
Half of Britons today are Londonis!
That londoni chick speaks Bengali so bad. My fart sounds nicer.