Manglish is a combination of the words Malaysian and English. It does not mean that Malaysians speak "mangled" English. Most Malaysians who have the command of English know how to speak proper English and when and how to switch to Manglish. When does one speak Manglish? When one is in a more informal setting and wishes to converse in a casual manner. Then i seems so natural just to switch-lah and no need to bother about present tense, past tense, when kind of tense, so one kind one. Summore-ah if everybody is speaking Manglish and you speak in "English" English, you feel so one kind... that's when you switch to Manglish-lah. So nice man and so relek-lah.
For Manglish is not just a language, It's also a mood. One sometimes just feels like rattling away in Manglish. Becos why? Because just like a delicious glass of teh tarik, or a taste of durian, so shiok only-lah to be able to speak Manglish - like touching base, connecting, being Malaysian. So unik one! I say man!