In a disturbingly smelly environment, I’m a fathead! (5,2)

'i'm a fathead' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'in a disturbingly smelly environment' is the wordplay.
'in' means one lot of letters goes inside another.
'a disturbingly' indicates anagramming the letters (I've seen this in other clues).
'environment' becomes 'i' (I can't explain this - if you can you should give a lot more credence to this answer).
'smelly' is an anagram of 'sllyme'.
'sllyme' going around 'i' is 'SILLY ME'.

Can you help me to learn more?