The act of spitting out beer/liquor/other alcoholic beverages upon attempting to chug any amount of them.

When you say something you dont mean without knowing your saying it

Spit up (or past tense, spat up) is a small bit of puke, usually the size of a quarter, but very rarely bigger, that would be classified as vomit. Typically happens in vurps or in very light nausea stages.