While commonly meaning to severely injure someone, to merk can also mean to eat large quantities of food in a very short span of time, usually while under the influence of marijuana. Because of the effects of marijuana, one is usually unable to stop eating for quite some time, and substantial amounts of food can be eaten.
Merking is usually done to food which is delicious, but not particularly healthy for you. McDonalds, donuts, pancakes, ice cream, and other things of that nature.
Where as one usually merks food, one can also merk a kitchen, which simply means to eat everything in that kitchen.
"Haha, I can't believe we bought 4 dozen donuts and merked them all!"
"Um, sorry I merked half your kitchen last night, man."