Bismillah ArRahman ArRaheem
Wa-Alaykum As Salaam
With regards to your question: " do i collect any sins also for discussing about the sins he committed in a jokingly matter?".
The short answer is no.
The long answer.... sins can not be discussed in a "joking manner" as they reduce the significance of the sin and they become "normalised". The mere fact of talking about a sin and admitting to it is not recommended let alone joking about them.
The issue of forbidding evil and enjoining good comes in to play here and there are rules that need to be followed with this regard, and they are the following five:
1. You must know the rules that adhere to the topic of discussion - what is good and what is evil, and be able to distinguish between them.
2. You must deem that it is probable your friend will heed your advice. So if you know you will not have an effect, you have no obligation, although it is better to somehow express disapproval.
3. Your friend must have the intention to continue to sin. So if it was a one off and unlikely to be repeated there is no obligation to proceed.
4. Your friend has no legal excuse (ie he is not being forced and is sane etc...)
5. You must not be in danger yourself, your family, or your property when enjoining good and forbidding evil.
So it seems the second point comes into play here in that your friend may be unlikely to listen to what you have to say and will continue to do what he does. One way to show your disapproval is to disassociate yourself from him. Given you have identified him as your "best friend", that is easier said than done, but the flip side of the coin is - who do you want to associate with? Remembering the advice from the Prophet, peace be upon him and his Purified Household,
*“Man imitates his friends. Hence, you must consider them whom you want to befriend.”*
And that of Imam Ali Peace be upon him,
*"He who believes in Allah and the Final Day should not fraternize with any disbeliever or associate with any sinful. He whoever fraternizes with a disbeliever or associates with a sinful one is certainly regarded as disbeliever and sinful."*
See here <https://www.al-islam.org/ahlul-bayt-ethical-role-models-sayyid-mahdi-sadr/rights-friends#fref_ea1739d9_5> for more on the topic of friends.