Konbanwa（こんばんは） is a Japanese greeting word used in the evening and at night. Although many non-Japanse people know and use it, sometimes the usage of the word is not normal.

Konbanwa is not a word for greeting to someone you know well, such as your family, friends, or colleagues. If a friend of mine says konbanwa to me, I feel odd. (cf.kon’nichiwa)
 
Saying konbanwa to your friends is not rude at all, but your friends may feel like being said “good evening” from you. Since English is not my native language, I’m not sure whether the example is proper. But I think my guess is almost right because I have never seen “good evening” to friends in English dramas or movies.
 
Among the three most well-known Japanese greetings, ohayou, kon’nichiwa, and konbanwa, konbanwa is the least used word these days. To my impression, Japanese people tend to say the word less and less.
 
Rule:
Like kon’nichiwa, don’t say konbanwa to someone you are familiar with.
 
Konbanwa is NOT used to…
 
・family members
・friends
・colleagues