... YA novel if: you're sixteen and dealing with things that fill you with angst.
... YA paranormal romance if: you're sixteen and in love with a vampire/werewolf/fairy/angel/fallen angel/telekinetic. And it fills you with angst.
... mystery novel if: you trip over at least one dead body in the first three chapters, and then someone makes a comment about how they do things on CSI.
... romance novel if: certain naughty bits on you and/or your irresistible love interest are heaving, throbbing, surging, etc.
... historical romance novel: if this occurs while the lace of your bodice is ripping, and/or someone makes a double-entendre involving his sword.
Please add to the list!