"Dis" is different. In the last few years, there has been an upsurge in people saying/writing "this" as "dis". It appears to stem from the desire of some (mainly young) non-black people to sound "black". Now before I get lambasted for any kind of racial stereotyping here, the pronunciation does appear to come from the stereotyping of a lot of black people in films and in rap music.
I have heard groups of teenage white kids in the UK speaking to each other and, if you couldn't see them, you would think they were black.
It appears that this is seen to be "cool". It seems to up there with the current trend for wearing your jeans around your thighs.
It is not restricted to "this". My friend's teenage son once sent my friend a text which read "Hey dad, whassup. Got dis sic guitar for xmas. Dat is jus wicked". Honestly, I nearly cried!
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