To come uninvited, oddly, is not bad mannered! (7)
I believe the answer is:
intrude
'to come uninvited' is the definition.
(I've seen this before)
'oddly is not bad mannered' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
'bad mannered' becomes 'rude' (I am not sure about this - if you are sure you should believe this answer much more).
'is'+'not'='isnot'
The alternate letters of 'isnot' are 'int'.
'int'+'rude'='INTRUDE'
Can you help me to learn more?
(Other definitions for intrude that I've seen before include "Be unwelcome guest" , "Butt in, interfere" , "Come in uninvited" , "Break in" , "Push in uninvited" .)