Is it:
onomatopoeia, the formation of a word from a sound associated with what is named
Something simple but hard to say,
Hard to pronounce, but it just means a word that sounds like the sound its describing
Contradicting myself but heard everyday,
No one hears the word 'onomatopoeia', but they hear what onomatopoeia is
Like finicky faucets that drip,
'Drip' is an onomatopoeia
Or tight trousers that rip,
And so is 'rip'
My applications often lead to people annoyed,
These sounds make people annoyed, like the buzzing of a fly
Maybe that's why my letters are rarely deployed.
Cause onomatopoeia is not a word that comes up often in conversation
However, if you know how I'm written,
Onomatopoeia is hard to spell
The sesquipedalians among you can't help but be smitten.
Sesquipedalians are people who like long words (or words with multiple syllables)