I just finished Jonathan Steinberg's biography (after devouring Pflanze's trilogy) so here's the answer:

John Motley, the man with whom Bismarck became close friends during their time as students at the University of Göttingen, wrote the novel "Morton's hope". The protagonist of this novel, Otto von Rabenmarck, was loosely (and thinly disguised) based on Otto von Bismarck. There are multiple passages in Morton's Hope in which von Rabenmarck engages in duels and picks fights with other (older) students and while the novel itself isn't necessarily a literary delight, it provides an extraordinary portrait of Bismarck.

Steinberg writes:

Erich Marcks, who in 1915 published the first full biography of Bismarck which used interviews with the living Bismarck, seems to have been one of the few German biographers actually to have read Morton's Hope. He concluded that 'out of the features of the Göttingen student Rabenmark, Bismarck stands out with unmistakable accuracy; his experience, his appearance, his way of speaking shimmer through'. Marcks also reports that Bismarck, in three semesters, engaged in twenty-five duels.

Jonathan Steinberg. Bismarck: A life (Oxford 2011) 40-41.

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Steinberg illustrates Bismarck's conflict-seeking nature with these passages. I'll cite one of them:

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(...) even then young Bismarck stood out. Motley/Morton then ran into Rabenmark (Bismarck) walking his dog, Ariel. Both man and dog are dressed outlandishly and, then a group of four students laugh, von Rabenmark challenges three of them to duels and the fourth who insulted the dog is forced to jump over Rabenmark's stick like a dog. They go back to Bismarck's rooms.

Steinberg, Bismarck, 40.

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Now, that passage really brought a grin to my face. Bismarck did, as far as I know, only engage in duels during his student life though he came close to duels later on in life. The following passage describes his near-duel with Georg Freiherr von Vincke (1811-1875), a deputy from Hagen in Westphalia in the Prussian Lower House.

Vincke, a fiery character, was widely regarded as the 'greatest Prussian parliamentary orator' of his generation and, like Bismarck, had been 'a dashing swordsman' as a student. Vincke loved to goad Bismarck. Bismarck explained the story to his mother-in-law. In a debate in the Prussian Lower House, "He [Vincke] accused me of lacking diplomatic discretion and said that so far my only achievement had been the 'burning cigar'. He referred to an incident in the Bund Palace which I had recounted to him in private 'under four eyes' as something trivial but rather funny. I replied to him from the podium that his remark exceeded not only the boundaries of diplomatic discretion but even the normal discretion that one had a right to expect from every properly educated man. The next day through his second, Herr von Saucken-Julienfelde he sent me a challenge to a duel of four bullets. I accepted after Oscar's proposal to use sabres had been rejected. Vincke asked for a 48 hour postponement which I agreed to. At 8 on the morning of the 25th [of March] we drove out to Tegel to a lovely spot on the alkeside. The weather was so beautiful and the birds sang so merrily that all sad thoughts disappeared as soon as I got there. I had forcibly to avoid thoughts of Johanna for fear of weakening. With me I had brought Arnim and Eberhard Stolberg and my brother, who looked very depressed, as witnesses... Bodelschwingh (a cousin of the minister's and Vincke's) served as neutral witness. He suggested that the challenge had been set too high and proposed that the duel be reduced to a shot each. Saucken speaking in Vincke's name accepted that and further announced that they would be prepared to withdraw the challenge if I apologized for my remarks. Since I could not in good conscience do that, we both took our pistols, shot on the command of Bodelschwingh and both missed... Bodelschwingh shed tears... the reduction of the challenge annoyed me and I would have preferred to continue the fight. Since I was not the person insulted, I could say nothing. That was it; everybody shook hands.

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Otto von Bismarck may not have lived after 25 March 1852, if Carl von Bodelschwingh had not lowered the stakes.

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Steinberg, Bismarck, 120.