Pteppic inhuming a pyramid and all of Djelibeybi's gods.
The manner in which Pteppic pulls it off is pretty spectacular in itself; he assassinates a reality warping pyramid and several hundred colossal and very angry Gods by holding a single, tiny throwing knife in just the right place at exactly the right time.
The Discworld Wiki summed it up brilliantly;
Poised on top of the Great Pyramid, at the highest point of the Kingdom, Pteppic is about to perform the greatest act of assassination ever: an entire Kingdom, seven thousand years of history, and an entire pantheon of gods. (And also, by default and by their implicit consent, a total of 1,300 monarchs... simultaneously.) The Assassin Guild's collective heart must have swelled with pride...
The Assassin's test. Yes, it's funny as a parody of a driving test, but don't tell me you weren't thinking that everything Teppic did was awesome.
Ptraci as Queen. Hoot Koomi wants to be an Evil Vizier and Ptraci is having none of it. She, in fact, assigns him the pointless rituals so that she can do the big important stuff. Then there's the way she tells him. "Do it yourself. You look like a man who's used to doing things for himself if I've ever seen one."