Be respectful but very direct
eg. 'this is my decision, and I'm using the camera I enjoy using'
If he tries to divert it to a 'you should AAAA because of BBBB', then you again be very direct
, reverting to your previous statement 'as I've said, it's my decision, and I'm using the camera I enjoy using."
ie. you back up your original statement, with a similar statement
If it keeps on, the conversation starts becoming about the ongoing conversation: eg "We've had this conversation before. I've told you that this is my decision, and I use the casio because I enjoy it."
If it goes on yet still, you repeat, and add "Please respect my decision"
The further it goes on, the more it becomes about the ongoing conversation eg. "we keep having this same conversation. I've told you I've made my decision. Please respect my decision"
If it goes on "This is becoming frustrating. I've told you numerous times I've made my decision. Please respect my decision"
As you can see...the longer it goes on...the more you reinforce your decision, and the more the conversation becomes about:
- him ignoring your decisions
- then disrespecting your decisions (constant ignoring is disrespectful)
- then about the repercussions (it becomes frustrating and a wedge in the friendship)
That structure can be used for conversation about any ongoing negative behaviour .