Your quickest checkmates... :)

Here is mine, 3 Moves: http://en.lichess.org/R6mX33rCGzGO

I made this one few seconds ago.
http://fr.lichess.org/tKWJ216N/black#14

My fastest, albeit not that fast...

I find that many lower rated players (Like myself, sometimes. Talking about players in the 1600-1800 FIDE {This is me guessing, I have no official rating, but when I play my maths teacher, who is approx. 1650 FIDE, we usually have even scores, although he is better equipped opening-wise}) tend to make these mistakes of not looking for the purpose of every move, even the innocent looking ones.

http://en.lichess.org/Gmkce4ZS3cps

Another one for me today.
http://fr.lichess.org/FUTlUPNy/white#15

Not the quickest and only a bullet game, so the game is esentially trash, but pretty checkmating combo. I saw a similar one in a book some years ago :)

I got Legal's Mate for the first time in many years: http://en.lichess.org/YVmzE4VgdTwO

(and my fastest classical win - vs. a 1800)

I had this mate against one of my older students (he is probably 75?) Something like that. I was teaching him at the time playing the caro since he was losing with e4 c5.

So by this time we had played probably 10ish games in the caro and he was at least not losing in the opening. I was trying different moves / variations each time and he fell for the trap.

1. e4 c6 2. d4 d5 3. Nc3 dxe4 4. Nxe4 Nd7
5. Qe2 Ngf6 6. Nd6#

Against various people probably 20 at least I have had this exact same game. Its not very good for white and I would never play this way in tournaments but in blitz that I don't really care about ill play super aggressive and have fun.

1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 Nxd5
5. e4 Nxc3 6. bxc3 Be7 7. Bd3 O-O 8. Nf3 b6
9. e5 Bb7 10. h4 c5 11. Bxh7+ Kxh7 12. Ng5+ Kg8
13. Qh5 Bxg5 14. hxg5 f5 15. g6 Re8 16. Qh8#

This is another one I have had happen even otb against a 900. Played it several times online too.
1. d4 d5 2. c4 dxc4 3. Nf3 Nf6 4. e3 a6
5. Bxc4 Bg4 6. Ne5 Bxd1 7. Bxf7#

Checkmate in 4 moves! :)

I did it when I just opened my account four months ago :)