A position from one of my games. I may be missing something, though. (Either it isn't mate or there's a quicker way?)

It' definitely mate and I don't see any quicker way. Another interesting line is :

In response to Rixo: Cool line... and if the rook moves anywhere else instead of 5... Rb8, 6. dxc7 and then 7. Ke7 Qd7 or 7. Kxe5 Qe4 mates (actually, Qe4 mates here, too, but it's nowhere near as cool ). 

Well, it sounds like you get it, but, for clarity, I would point out that mate is not forced here. 1. d5 Bxd5 2. Qxd5 (otherwise backrank mate) Qxd5 2. Rxd5 Ke6 and Black will live for more than 7 rounds, which isn't saying much, I'll be the first one to say!  Peace!

1. d5 Bxd5 2. Qxc7 Ke6 3. Qd6#

Qxd5 isn't forced.

Here is another line:

6. Rxf8 leads to mate in two after 6... Qxg2+ 7. Rxg2 a5 8. Qd6#, slightly faster than  mate in four after 6. d5+, but still eight moves total. Nice variation.

After 2...Ke6 it could've gone 3. dxc+ Ke7 4. Qd6+ Kd8 5. Qd7#

2... Ke6 3. dxc+ Bxc6 breaks the mate, actually.

Nice  One!!!!!!!!!!!!!!!!!!!Cool!!!!

I think this line is also possible:

To 2n_2n: 4... Kg6 escapes the mate.

didn't see that one. sorry. thanks for the correction.