I need ideas against 1.d4 2.Nf3

I always play as black against this guy who plays always the same: 1.d4 2.Nf3. I usually play 1...Nf6 2...e6 3...d5, and sometimes 1.f5. Can anyone suggest some ideas both sound and funny to play?

You've got to elaborate further than that.  How does he follow up?  3.c4? 3.Bf4? 3.e3? 3.Bg5?

You say you play 1...Nf6 and 2...e6.  After 1.d4 Nf6 2.Nf3 e6, what does he play?

3.c4 leads to the Queen's Gambit Declined (3...d5 4.Nc3), Catalan (3...d5 4.g3), Benoni (3...c5 4.d5), anti-Benoni (3...c5 4.Nc3), Queen's Indian (3...b6) or Bogo-Indian (3...Bb4+).

3.Bg5 is known as the Torre Attack

3.Bf4 is known as the London System

3.e3 is known as the Colle System

They all have different ideas and you need to understand all 4. 

Hope this helps in directing your research.  What you normally do after 1.d4 Nf6 2.c4 should somewhat drive your decisions.

Thanks for your answer, I put some examples of our games. 1-

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5-

6-

He always goes the same: 3.c4. I´ve tried 3...Be7 then he goes 4.Nc3, but if a give the check 3...Bb4+ he covers with Bd2. Could I try something else? (besides the Dutch)

The first diagram is the orthodox QGD.

Your others are littered with errors.

For example, 1.d4 Nf6 2.c4 e6 3.Nf3 Bb4+ (same as yours - just invert White's 2nd and 3rd move) is known as the Bogo-Indian Defense.  4.Nbd2 is best answered by 4...c5 and 4.Bd2 is best answered by 4...a5.

Also possible is 3...d5.  Now if 4.g3, this is known as the Catalan.  You can play the Open Catalan, 4...dxc4, Closed Catalan, 4...Be7 5.Bg2 O-O 6.O-O c6, or the deferred open catalan, which is the same as the closed except 6...dxc4 instead of 6...c6.  Another Option is the Bogo-Catalan, which is 4...Bb4+, and here, after 5.Bd2, here you do go back to e7.  The B on d2 is misplaced in the Catalan, but that is vastly different than the Bogo-Indian.

The other option after 3...d5 4.Nc3 (instead of 4.g3) is 4...Bb4, known as the Ragozin variation.  You can, of course, also just play the QGD with 4...Be7.

I would recommend investing in a book on the QGD, Bogo-Indian, or Ragozin, along with the Catalan, to understand these defenses.

The last option is 3...b6, known as the Queen's Indian.  However, if you play the Queen's Indian, you have to understand it only works against 3.Nf3.  If 1.d4 Nf6 2.c4 e6 3.Nc3, white threatens e4, and so 3...b6?? 4.e4! Advantage White!

Black must instead play 3...d5 (QGD), 3...c5 (Modern Benoni), or 3...Bb4 (Nimzo-Indian).

c4 always

if 2.c4 lemme introduce the best opening for beginners

- benko gambit

Sure, the Benko and te Benoni are funny, but he never plays 2.c4

Thanks @ThrillerFan for your advice!

Maybe I´ll study a bit the Queen´s Indian and give it a try the next time.