The move 3...f5?! in Owen's Defense (1.e4 b6 2.d4 Bb7 3.Bd3 f5?!) has been played and analyzed for almost 400 years. Greco-NN, Rome 1619 quickly concluded 4.exf5! Bxg2 (the point, trapping White's rook - if Black can survive White's attack) 5.Qh5+ g6 6.fxg6 Nf6?? 7.gxh7+! Nxh5 8.Bg6#. Staunton pointed out the improvement 6...Bg7! in The Chess-Player's Handbook (1847), page 379. He analyzed 7.gxh7+ Kf8 8.hxg8(Q)+ Kxg8 9.Qg4 Bxh1 10.h4 e6 11.h5, with advantage to White. Over 120 years later, 10...Bd5!? (Schmid-Vitolinsh, Latvia 1969) and 10...Qf8! 11.h5 Qf6 12.h6 Rxh6 (Hendler-Radchenko, Kiev 1970) were shown to be playable for Black. Similarly, in Lombardy-Regan, U.S. Open 1974, the 15-year-old Regan got the advantage after 10.Nc3 Qf8! 11.Be3 Qf6 12.h3 Qh4 12.Qg6 Nc6. (Lombardy demonstrated why he's a grandmaster and we're not, holding a draw in an ending two(!) exchanges down.)
Alas for Black, later analysts convincingly refuted 3...f5? in two different and surprising ways. Accordingly, the French GM Christian Bauer now calls the move "simply suicidal" (Play 1...b6, p. 5). In both lines, White disdains the immediate capture on g8 and instead attacks Black's king. It is important to learn at least one of these busts so that you can refute 3...f5? if someone plays it against you.
In the mid-1970s, F.A. Spinhoven of the Netherlands found 8.Nf3!! Nf6 (8...Bxf3? 9.Qxf3+ and 10.Qxa8; 8...Bxh1 9.Ne5! Bxe5 10.dxe5 Bd5 11.hxg8(Q)+ Kxg8 12.Qg6+ Kf8 13.Bh6+) 9.Qg6! and now (a) 9...Bxh1 10.Bh6! Rxh7 11.Ng5! Bxh6 12.Nxh7+ Nxh7 13.Qxh6+ with a crushing attack or (b) 9...Bxf3 10.Rg1! Rxh7 11.Qg3!! ("the soul" of 8.Nf3!! - Soltis) Be4 12.Bxe4 Nxe4 13.Qf3+ and now White is a pawn up, with a winning attack, after 13...Kg8 14.Qxe4, or an exchange up with an easily winning position after 13...Nf6 14.Qxa8 Rxh2 15.Bf4 Rh4 16.Qg2 Rg4 17.Qh2 (Boris Avrukh, 1.d4, Volume Two, p. 551).
In 1982, Guido den Broeder found an alternative refutation, the stunning 7.Qf5!! Nf6 8.Bh6!! Bxh6 9.gxh7 Bxh1 10.Qg6+ Kf8 11.Qxh6+ Kf7 12.Nh3! and Black was quickly annihilated in den Broeder-Wegener, corr. 1982. See Wikipedia for more details. John Watson writes that den Broeder's 7.Qf5!! and Spinhoven's 8.Nf3!! both win, but that the analysis of 7.Qf5 "is complicated," while 8.Nf3 "is clearer" (Mastering the Chess Openings, Volume 4, p. 96).
Here is an online game I played yesterday. Unfortunately for my opponent, I was able to remember Spinhoven's analysis. Black played the latter part of the game weakly, but had an objectively lost position in any event.