A screaming baby paired with "congratulations"? Ah, that's subtle sarcasm at its snarky finest.

Here's a tip gleaned from years of family reunions: the second Mrs. Klass asks "What's that supposed to mean?", it's time to leave. Trust me.
Of course some cakes are more subtle, like this one:

"We'll wish you luck, but we don't have to be happy about it."
Or just baffling, like this one:

I'm not sure if this guy is supposed to look afraid of being eaten, disapproving, or in pain from his "shades" melting onto his face. Say, there's a bit of unintentional ironic realism for you: sunglasses melted onto the face of the sun. Heh.
If Mr. Future's-So-Bright's feelings are ambivalent, though, these cookies are clearly ticked off:

Poor angry cookies. At least their pain is my sugary gain - and I get the added bonus of talking smack to my food. "What, you lookin' at me, punks? Huh? How's about I drown you in some milk before biting your heads off, then? Yeah, not so puffed up now, are you, tough guys?"
And finally [smirk],

Brittany M., Elizabeth G., Jessica C., Linda N., Monique R., and Jill C., many "thanks".