A spleenful person is irritable and spiteful. If someone is full of mean, snarky comments, criticisms, complaints, and general negativity, you could call them spleenful.
Spleenful is not a very common word in modern English. It's derived from the noun spleen, which is an important organ in the body that helps to form white blood cells and get rid of worn-out red blood cells. In ancient and medieval medicine, the spleen was thought to be the organ that produced "black bile," one of the four bodily humors that governed a person's temperament. Black bile was associated with a nasty, morose attitude. So spleenful is used to describe someone with a bad temper.