Beating a cocky person

This person said that it wouldn't matter how much time I take to think, s/he would still win.
So negative.

You were winning the whole time.
17 Ne4 would have won an exchange
20 Nd5 would have won an exchange
You gave him a chance to come back in the game with 21...d5 threatening to fork the pinned knight with 22...d4

congrats on your win! that's really cool.

your opponent played pretty suspiciously after Bg4, he basically has to give up his bishop for free after d5. That also puts him further behind in development since he's neglected his kingside while losing a tempo to trade too. Also, his a6 was blocking Bb5, so a4 by you was unnecessary - and you also missed an earlier Bb5 just winning on the spot. Lots of missed opportunities for you to grab the exchange too, completely missed by both players. Maybe you saw Qf5 after Ne4, but Nxd6 comes with check. After he castles, it's still possible to grab a big lead after Ne4 Qf5 cause the pawn on c7 has been just hanging there instead of on c6. and of course the hanging mate in 1, missed by both sides. Another tip is to capture towards the center with your pawns. It's very rare that capturing away is better (and usually in king's pawn openings). In this case you can build up a huge center and make it really hard for your opponent to have any central influence with your space advantage.

hope this helps!

Did they say something after their loss, by CHECKMATE