What are the differences between arrogant, conceited, pompous and boastful?

Arrogance:
Associated with personality. Arrogance also does not always mean 'rude', but sometimes this is the case. It is usually an internal feeling, meaning if they are rude, it's not on purpose.

Conceited:
Also associated with personality. However this time it is more connected to being rude - Conceitedness is to look down on others on purpose.

Pompous:
To go 'over board', to act 'higher up'. This just means the person is snooty - again, it does not mean they are rude all the time.

Boastful:
Self indulgent. Boastful is closely associated with the action of TELLING everyone what they did, or what they achieved.

These words are called 'Synonyms' = similar meanings.
However, a good vocabulary enables you to use the exact, right word--based on the subtle meaning that you wish to convey.

All these words convey descriptives of someone who is not likeable to others!

Arrogant & Haughty = a person who is very proud, and therefore is not liked by others.
Conceited = one who thinks very highly of HIMSELF! This person too is objectionable.
Pompous = a person who is showy and indulges in a lot of pomp and show; gradually, this word has come to mean a guy who thinks no end of himself!
Boastful = the fellow who boasts and often makes wild claims TO OTHERS about his achievements.

You now understand connotation vs denotation, so you want the color of words

Arrogant is someone who is aggressively proud as to what they do

Conceited is more smarmy, as though you should bow down to them

Pompous is conceit light, but with more hot air and less to work with

Boastful I feel is more desperate, trying to prove something they cannot

arrogant think they know everything, conceited think what they have is the best,pompous expects adoration,and boastful are windbags of condescention

Pompousness