How much would be considered as a "large amount"?
RM100k and above?

Really? So low? 
Personally, I have transferred up to RM40k without anyone calling me from the bank.
The only one instance that I received a call from the bank, was when I had around RM180k or something transferred to my Maybank account from Hong Leong bank (balance from the proceeds from the sale of an apartment).
Maybank called me, and I just told the lady that this was the balance amount from the apartment sale, after HLB had deducted the remaining loan balance.
She just said OK, thank you very much, and that was it.
No declaration, no filling up forms, no supporting documentation or any such nonsense.

I think he transfer in using bitcoins. So since not many people in malaysia using bitcoins, so they close eyes.

Btw, have you use money changer to transfer money out of malaysia before?