To avoid vomshitting one must not over push his shit instead relax and let your anus do its buisness.
Another advice woulf be decresing the amount of drinking alcohol and decreasing masturbating.
2) The word is said in a situation where someone is shocked and grossed out from the person he's speaking to. So the person will reply by saying "Are vomshitting me?" becasue that person had an erge to vomit due to the disgusting and shocking thing that was told to him.