when someone is blabbing off at the mouth and you want them to shutup the phrase 'dot com' is basically used to shut them down.

1/if someone says something stupid they can quickly redeem themselves by saying, "dot com."
2/you can say "dot com" right after someone says something retarded to call out their stupidity

To spread information around, as on the internet.

We say dot com when something starts getting complicated, It is normally said in a humorous manner.