Get rid of last weed with one exclamation of annoyance (5)
I believe the answer is:
ditch
'get rid' is the definition.
(I've seen this before)
'last weed with one exclamation of annoyance' is the wordplay.
'last' says to take the final letters.
'with' is a charade indicator (letters next to each other).
'one exclamation of annoyance' becomes 'itch' (I can't justify this - if you can you should give a lot more credence to this answer).
The last letter of 'weed' is 'd'.
'd'+'itch'='DITCH'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for ditch that I've seen before include "drainage feature" , "Throw away (sl.)" , "give up" , "Get rid of; dug channel" , "Moat" .)