Rick might be the smartest man in the multiverse, but he's also one of the most demented. Rick lives in a world of high stakes and high rewards, and he's definitely open to cracking a few eggs in order to make his science-omelette. The ends always justify the means in Rick's mind, even if the means end up destroying entire planets in the process.
Throughout the series, Rick has done a lot of objectively horrible things. He's not known for beating around the bush or being subtle about his opinions, and his actions speak even louder than his words. Sometimes he can be a bit passive-aggressive though, so he's not above being low-key in his debauchery either. He's open to casually exploiting an entire universe at once or even cloning his loved ones and exploiting them. This is a breakdown of Rick's most low-key cold-blooded acts in Rick and Morty, ranked by how subtly evil they are.
The episode "Rick Potion #9" sees Morty trying to score a love potion from Rick to give to his crush, Jessica. Morty's creepy desire ends up turning the entire world into lustful, Morty-obsessed monsters. Rick tries several times to create an antidote, but each iteration makes the population of Earth even more monstrous.
Eventually the entire planet is covered in Cronenberg-like monstrosities, with the only people immune being Morty's immediate family. Rick just sort of throws his hands in the air in defeat and decides to abandon that reality, including Beth, Summer, and Jerry.
We know that Rick is willing to take advantage of people, but his actions in "The Ricks Must Be Crazy" show that his manipulation skills can be downright biblical. After the microverse battery in his ship stops working, we learn that it actually houses an entire artificial universe that Rick created. The entire universe only exists to power his ship, but it has given birth to societies as complex as our own.
Rick even meets an intellectual rival inside the battery, but refuses to acknowledge him as a peer. Instead, he threatens him by saying that his entire universe will be destroyed if they don't keep providing him with power. He effectively enslaves an entire tiny universe just to keep his ship's headlights on.
Rick is rarely nice to Jerry, so it's a surprise when he includes him on an adventure in "The Whirly Dirly Conspiracy." It's mostly because Morty is worried his dad might off himself after the divorce, but it does bring the two of them closer together. Unfortunately, Jerry is captured by a militant named Risotto Groupon, and he learns that Groupon's people were enslaved because Rick carelessly sold devices to their enemies.
It's not uncommon for Rick to sell extremely deadly instruments on the black market, and he's clearly open to dealing with shady characters. It's sobering to think of the countless lives that have been indirectly ended because Rick wanted to make a quick buck.
"Pilot" Rick is different in a lot of ways from current Rick. He's a bit kookier and less overtly nihilistic, but he still treats Morty like an expendable subordinate. The peak of his maltreatment comes when Rick asks Morty to store a Mega Seed where the sun don't shine. Morty is obviously horrified by the request, but Rick insists that it's the only way they can make it through intergalactic customs.
Furthermore, the only reason they even needed to go through intergalactic customs is because Rick accidentally blew his portal gun charge by getting side tracked in an alternate dimension. It's a pretty big ask of Rick when he's the reason they're stuck in the first place.