Ok... Ok... I know you don't like UML...

But, if you need to draw a pretty quick Sequence Diagram, you should consider using site that Phillip showed me today.
It took me less than 15 seconds to draw this diagram:

It has a specific language to draw it:

Phillip->Fabio: showSequenceDiagramWebSite()

note right of Fabio: Thinks it's interesting

Fabio-->World: blogAboutIt()

Give it a go...