What things will kill FPS?

Including any LUA coding.

Bombs? Gbombs3 lag like hell when you spawn like 5 smoking bombs… uugh.

Prop spam, Explosive spam, Nuke spam, etc.

Anything, there more there is of something, the lower ya fps will go

Ragdolls. Or even corpses if they are in the thousands.

Dynamic lights.

Playing with more than 3 people and using a ragdoll.

NPCs, especialy online