In the first meeting between Thanos and Darkseid, the Mad Titan's first words to the ruler of Apokolips actually showed he respected his fellow villain. In a Marvel and DC Comics crossover that saw the two big bads face off, Thanos referred to Darkseid as the "Lord of Destruction," showing that he took his opponent very seriously. Unfortunately for Thanos, Darkseid didn't share mutual respect, immediately insulting the Marvel villain.
Thanos and Darkseid are the ultimate villains in the Marvel and DC Comics universe, as their quests for power have pushed the greatest heroes to the brink. Thanos' fight with Earth's Mightiest Heroes with the Infinity Gauntlet in his pursuit of Death's affection resulted in half of all life in the universe being snapped out of existence. Meanwhile, Darkseid's efforts to seek out the Anti-Life Equation have led him to acquire the powerful formula and use it to wreak havoc across the galaxy. In a crossover comic between Marvel and DC Comics, Thanos showed surprising respect for Darkseid, which ultimately wasn't shared.
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In the crossover Marvel Comics Versus DC #2 by Peter David, Claudio Castellini, Dan Jurgens, Paul Neary, Joseph Rubinstein, Bill Oakley, and Gregory Wright, two cosmic entities pit the DC and Marvel Universes against one another with fights between their superpowered inhabitants - with the winner's universe getting to live. Amid the battles, Darkseid and Thanos meet, where the Mad Titan offers a wager to the DC supervillain. He asks Darkseid if he'd like to make a wager on the fights, showing respect by referring to him as the "Lord of Destruction."
Unfortunately for Thanos, Darkseid doesn't share the same respect for the Marvel villain, as he refers to him as a "pale imitation" who will lose their wager. While readers have never seen Darkseid and Thanos fight like the many matchups in the DC vs. Marvel crossover event, the fact Thanos is willing to refer to him as the "Lord of Destruction" shows that he understands what a powerhouse the ruler of Apokolips truly is. However, Darkseid doesn't see Thanos as anything more than a cheap knock-off.
Darkseid and Thanos will forever be tied to one another, as they are the ultimate cosmic villains in the DC and Marvel Universe, respectively. But, in the crossover comic, Thanos' first words to Darkseid showed a surprising amount of respect - and not at all combative - that he doesn't often extend to many other villains. In the end, Thanos' respect wasn't reciprocated, as Darkseid made sure to insult the Mad Titan by referring to him as a "pale imitation" of himself. Ouch.