It's clearly not a tongue, just the inner mouth being red. It's open, because the bomb is excited, not sticking it's tongue out like it's saying "whatever, it's all silly".
:D rather then :p
I would say it is clearly a tongue, because it extends beyond the confines of the head.
I asked Dave... let's settle this once and for all:
Thank god. I always saw it as a mouth. I didn't even think of looking at it differently until I came to this thread. And then I was getting really worried I'd never be able to look at it right again. Everything was weird for a moment.