Can you cast dragon’s breath on yourself?

Yes you can

Not only can you.....

You should. All the time. It's a neat party trick.

Thanks 

You can, but my wizard who knows it and who keeps it prepared doesn’t. He casts it on a team mate who doesn’t do much melee damage instead of casting it on himself. It’s really a melee spell and wizards should usually avoid melee. 

Cast it on your familiar. Cast it on your friends. Cast it on yourself and then get someone to make you invisible.

The fun never stops... until a minute it up.

You can, yes. But you might want to cast it on your familiar since it requires no Attack Roll it gets around the “familiars can’t attack” rule and then your Spider can breath fire!