Cerberus: You, a mere human, make a mockery of ME?!? *breathes a ray of ice, which Dante dodges*
Dante: Eeeasy, Fido. How 'bout I take you for a walk? *claps hands and makes a beckoning motion* Come on, puppy, let's go.
Jester. Creepy Awesome, campy and maniacal, (complete with Joker-esque evil laugh) appears randomly out of nowhere to give advice, and threatens to spank you during the boss fight. Depending on whether you're afraid of clowns, that is either traumatic or hilarious. He also subtly breaks the fourth wall and does the Charleston while trying to avoid ludicrously rapid gunfire from Dante, who finds him annoying because "I don't like anyone who has a bigger mouth than me."
When Dante receives Agni & Rudra in DMC 3. He agrees to take them with him on the condition that they don't talk. Afterward, he does his usual showoffy weapon display, after which:
Dante: *looks at them, then clonks their heads together*
Dante: No. Talking.
*silence from the two swords*
Dante: ...Good. *sheaths them and walks on*
Dante acquires Nevan. Instant rock show.
DMC 3: After Dante does his midair motorbike-fu thing. He lands inside the tower, unharmed...and the bike explodes. The explosion clears, he looks at the handlebars (which he is holding; the handlebars are the ONLY PIECE left), grunts, and casually tosses them over his shoulder as he leaves. Clank.
Dante's reaction to Arkham assuming the form of Sparda:
Dante: It's like staring into a backed-up toilet. Why do you always stick your nose in other families' business? Come on, dude, don't you have any hobbies?
Devil May Cry 4
Nero meeting Agnus for the first time in his laboratory after calling it a hellhole. Agnus yells at him to watch his words and the following dialogue ensues.
Agnus: Just as foul-mouthed as I had heard. The rumors prove true. As will the new ones concerning your d-d-d-demise.
Nero: Don't you think that's a little harsh? Killing me because of the way I t-t-t-t-talk?
DMC 4 has Dante meeting Gloria, and what does he do? Laugh at her because "that regal look suits her". This is because he knows she is Trish.
Same thing with Sanctus saying "Oh, it's you... Gloria," when Trish is not in disguise.
So Nero's walking through the forest one day, when suddenly...
Dante: WHAT THE HELL IS THIS?!?
And then later, when Dante is taking on the Echidna... She shoots her seed pods at him, and he kicks them right back at her. After they bounce off her head...
Echidna: What the....( and the last pod hits her, which leads her saying in a supremely pissed off tone) Who the HELL are you?!
DMC 4: The Saviour is revealed, and it's a gigantic creature that would normally herald a Mass "Oh, Crap!" from the cast of any other game. Dante's only reaction is an unimpressed "Check it out. It's got wings!"
Trish agrees. "The design shows a terrible taste."
Dante acquires Pandora. After it turns into a few different ranged weapons, it turns into... Dante closes the lid hastily, breathes a sigh of relief, and the floor just breaks.
Speaking of which, before acquiring it, Dante faces Daegon. Unlike how Nero meets Bael's 'lures' for the first time (since they're the same kind), Dante is VERY happy to see Daegon's 'lures' and even tries to flirt with them. But he manages to avoid Daegon's attack thus leading to this conversation:
Dagon: What? How did you know?
Dante: You can hide your body, but that smell...Hoo! There's no covering that up.
Dagon: Insult me one more time and I'll make you suffer more than you though possible.
To be frank, ANY battle that involves Dante fighting with the previous bosses that Nero didn't kill are epic.