Merriam-Webster

fib : pretentious nonsense

1811 Vulgar Tongue

A fib, or falsity.

Merriam-Webster

An impressive, pompous, or fashionable air or display : a person dressed in the height of fashion : a person of high social position or outstanding competence

1811 Vulgar Tongue

A gentleman. A well-dressed map. The flashman bounced the swell of all his blunt; the girl’s bully frightened the gentleman out of all his money.

To drink before a journey.

–Cut from the definition of liquor from the 1811 Dictionary of the Vulgar Tongue.

It depended who was saying this, as to what it would mean.

As in “a lion of the ton” – something someone in society might say:
A person of outstanding interest or importance

–Definition from Merriam-Webster

Used in cant – something a person on the street might say:
To tip the lion; to squeeze the nose of the party tipped, flat to his face with the thumb. To shew the lions and tombs; to point out the particular curiosities of any place, to act the ciceroni: an allusion to Westminster Abbey, and the Tower, where the tombs and lions are shown. A lion is also a name given by the gownsmen of Oxford to an inhabitant or visitor. It is a standing joke among the city wits to send boys and country folks, on the first of April, to the Tower-ditch, to see the lions washed.

–Definition from the 1811 Dictionary of the Vulgar Tongue.