I like the taunt, and I think it fits the Demoman well. Here's some animating tips:

The "falling back" animation seems a big choppy. It'll get pretty annoying, but taking the extra time to add a few more frames of him sitting down will make it a lot better. Aside from that, maybe a little bit of extra detail to the feet. Other than that, it seems great. Also, add a few more "BUUUUUURPS" to him after he takes a swig ;)

(No seriously, demoman needs to burp :D)