Post A Letter Using Plastic Bag

My sister need to get my parent's signature to apply for PTPTN. The instruction is written that 3 copies of the form is needed, but my smart sis here sent only one copy back with her signature imprinted on the form. In fact, you can't photocopy the form which has a signature on it. Since she doesn't has a printer, I offer to help her to print out the form and pass it to her so that she can post it to my parents in Kuching.

Me: thn i help u print la
Sis: den I've to go to post office line up to buy the envelope again lar?

As you can see, both of us are in Melaka and she asked me whether to buy an envelope to post back to my parents or not. A pretty dump question, if you don't buy an envelope, then how on Earth can you post the forms back to my parents? So I reply back with sarcastic answers...

Me: no need to buy envelope, u pass to mum urself la
Sis: when?
Me: o u can use plastic bag n post to mum
Sis: u mean use pos express har?
Me: plastic bag
Sis: thn how?
Me: then paste stamp on the plastic bag
Sis: how to post use plastic bag
Me: write the address on the plastic bag, put in the mailbox la
Sis: need how many day reach their hand?
Me: wait for the postman to send
Sis: whr to buy the stamp ler?
Me: post office
Me: ngaiti... how you score so many A's in SPM?? OF COURSE USE ENVELOPE LARRRRRRRRRRRRRRRRRRRRRRR
Sis: y so kankor (troublesome)?
Me: abo use plastic beg meeehhhhh
Sis: u say use palstic bag ler
Sis: u sendiri say 1
Me: u ask me wan buy envelope to post o not
Me: i mar tell u use plastic beg
Sis: ooo...u cheat me har?
Me: you say leh?
Sis: duno o
Sis: use envelop ?
Sis: use pos express lar?
Me: you go ask mum can use plastic bag to post o not

*vomit blood*