Tennis, absolutely. How the heck did this get in in the fist place? Where does it even fit? Unlike most sports, tennis already has a fairly rigid hierarchy of prestige for its events, from the Grand Slam at the very top to the junior level events on the bottom. Olympic tennis is just superfluous, completely thrown in. If we’re going to have it, make it amateurs-only* so it at least serves some purpose.
Soccer, likewise. Just the fact that World Cup players are prohibited speaks volumes. Utterly pointless.
Boxing. A damned disgrace. Every single Olympiad, corruption and bungling and robbery, and this asinine electronic scoring just compounds it. A boxing gold medal carries slightly more prestige than a fantasy league championship, and pretty much the same future professional prospects. If we need an Olympic sport with lots of hitting, bring in rugby. At least that one has some excitement.
Racewalking. Never mind that it’s an activity that the world’s best can do only slightly better than you or me, the problem is that it has zero entertainment value. Even the completely sports-ignorant can appreciate the spectacle of a power forward delivering a soaring dunk, a linebacker breaking free and drilling a hapless quarterback to the turf, or a steel-nerved shotmaker hitting from the rough between two trees and sticking it 5 feet from the hole. Racewalking has a bunch of people making the same damn motions over and over and over and over, trot trot trot trot, and all the time an official constantly hovers nearby and flips up a big red circle every time he catches something amiss. I mean, do I even have to explain how much this sucks? No wonder this was the sport the Brothers Chaps ridiculed in a Videlectrix game.
As for some others…
Subjective contests: They’re fine. Really. I used to scoff at them myself, but I learned that pretty games have their place. The big problem was miserable girls forced to sacrifice their childhoods, and this has largely been fixed. What’s completely, utterly wrong is a judged event getting the SAME KIND OF AWARD as a real sport. Ribbons. Or plaques. Or slates. Or if it has to be jewelry, bracelets, pendants, necklaces, anything other than medals.
Equestrian: In addition to the obvious issue of who really deserves to be on the podium, has the problem of being available to only a tiny subset of competitors. I.e., rich enough to own, care for, and train a large animal. The Olympics, at their core, are about the raw basics of athletic ability. Running. Jumping. Swimming. Throwing. Lifting. There’s a reason the motto is “faster, higher, stronger” and not “we can afford stables and riding facilities and you can’t”. I don’t mind this as a spectacle, but again, have some other award and stop pretending that it means as much as the 100 meter dash.
Judo/Taekwondo: I’m fine with judo. In addition to giving us the immortal Ryoko Tani, it’s the perfect Olympic event…frenetically paced, weirdly scored, and full of confusing rules. 
Taekwondo, though, was obviously just pandering to Korea, and I honestly don’t see what it has that karate, mueitai, savate, kung fu etc. don’t. There should be an entirely different event, “international karate”, incorporating elements from multiple striking disciplines and flexible enough that different martial artists can adapt to it.
Basketball: First, I propose that the IOC finally acknowledge that what happened in 1972 does not deserve the idiotic and morally bankrupt term “controversy” but was instead one of the most brazen, naked robberies in history, of which there is more than adequate proof, and as there is no “statute of limitations” on getting the result of a gold medal game correct, the result of that game is hereby officially reversed. The surviving Soviet players can keep their hardware, as it was given to them in good faith and they are not at fault for this vile injustice, but the record book will show the correct, true, actual, proper, right result. Secondly, I’d like the IOC to issue an official ruling that any and all medals won by political entities that no longer exist…in particular, the Union of Soviet Socialist Republics and the German Democatic Republic…shall in perpetuity not be included in any way, shape, or form in the medal counts of any political entities that have either preceded or succeeded them, whether or not they shared the same geographic area or populace. Then we’re cool. 
- Just so we’re completely clear, I’m fully aware that the Olympics stopped being an amateur showcase decades ago (at least), and I’m fine with that. However, I’m all in favor of certain events being restricted to amateurs. Hey, we could have a different type of award for those as well!