Stuff up is a phrase that can be used to describe the act of clogging or blocking something. CLOG is a four-letter word that is often used in this context, and it means to fill or block a passage with an obstruction. This phrase is commonly used to describe the act of blocking a drain or pipe with an accumulation of material, such as hair, dirt, or other debris. It can also be used to describe the act of filling a space with too much material, such as stuffing a suitcase with too many items.