for the sake of clarification, double jeopardy is a defence that prevents an accused person from being tried again on the SAME CHARGES and on the SAME FACTS after being tried and adjudged. Example, he committed rape of A on 1.1.2017 and found guilty by court. You cannot charge him again for rape of A on 1.1.2017.

Your earlier question was "If he rape again in Malaysia..can he be charge again?", this means he is committing another fresh offence in Malaysia. In this case, he will be charged for this NEW offence. There is no issue of double jeopardy.

In your question, "in Msia if you commit the same offence twice...", you will be charged with TWO offences. No issue of double jeopardy as well.

Q1> Is it always necessary to make a police report if you intend to file a civil lawsuit for defamation?

NOPE. Not necessary for a CIVIL lawsuit.
Q2> How do you draw a line between an opinion and something that is defamatory?

Long story short:

An opinion is general statement expressing one's view.

Nevertheless, an opinion can be a defamatory statement, if the statement portray a bad impression of a person referred to in the public.
Example: statement made, "i think superman is dishonest", and this statement is published or circulated in the public. This tends to portray a bad image of superman, so it may be a defamatory statement.

There are always defences available such as justification and fair comment but it will all depends on the situation.

Cheers 

Old pipul like me sembang-sembang kosong in kopitiam where got qualifications. 

A nice kopi-O with roti bakar good enough ad.