Situation1: My close friends offer me 'something' that of no use for me. So I want to reject it by saying 'I have no need for 'that'.
(Situation 1-1: I want to sound really rude to my close friend as to show that we're really close that we really understand each other)
(Situation 1-2: I want to sound 'rude' to make this 'good friend' stay a bit far away from me, but not destroying the relationship to him)
Situation2: My parents offer me 'something' that of no use for me. So I want to reject it by saying 'I have no need for 'that'.
(Situation 2-1: I don't want to sound rude to my 'half-foster parent' in Japan)
(Situation 2-2: I want to deliberately sound rude to my blood parent)
Situation3: My professor offers me 'something' that I think has no value for the research development. So I want to reject it by saying 'I have no need for 'that'. (Can I just plainly reject him? - Notes: I still need him to help with the project, but I want to convey that his help/assistance doesn't really help with the project's progress)
How to say: "I have no need for 'that'" "Sorry, I don't need that"
Here are some examples I conjured up:
'that' は/が いらない
'that' は/が いらないです
'that' は/が いりません
'that' は/が いいです。
'that' は/が やっぱり 要らない/要りません
'that' は/が 結構です
1.Is there any 'set-phrase' that conveys in a more polite way or roundabout way in those three situations?
2.Is there any 'set-phrase' that conveys 'the same feeling' without conveying an apology or saying apologetically in those three situations? [ like: すいません/すみません/申し訳ありません]
3.How about this:
その必要はない -> Is this okay? or too rude?
Is there any set-phrase that we can use to include: '以外' for more natural Japanese?
If possible, please explain the nuances for every answer that you give so that we can learn something (especially from the natives) especially the cultural difference of rejecting offers/help from others. Thanks a lot for all your answers!