The Big Bang Theory is a controversial sitcom - many self-proclaimed nerds absolutely hate it, calling it insulting and ridiculous. However, as one of the most successful scripted shows on television and with twelve seasons under its belt, it clearly has some devoted fans. Love it or hate it, though, there's no denying that Howard Wolowitz is something of a problematic character.
From the start, he's a creep - and it's played off as funny, as he's obsessed with getting laid, even though he is truly terrible at approaching women. He has all kinds of ridiculous plays, but eventually meets his match in Bernadette, and the two fall in love, get married, and have kids. In some ways, Howard improves as the show goes on, but in others, he just keeps getting worse.
Creepier And Creepier
There's no denying that as Howard continued, he just got creepier and creepier. Sure, after meeting Bernadette, this was toned down a little as he stopped going 'out on the prowl'. However, in many ways, his behavior actually gets worse once he's in a relationship. At the start, he could be forgiven for many things for wanting to be in a relationship - but once he was in one, he lied to Bernie about his past and sexual history, and he even cheated on her (online, admittedly, but still). At that point, there's really no excuse.
Stopped Being There For His Friends
At one point in the early seasons, Howard intentionally triggered a potentially fatal allergy just so that Leonard could have an incredible surprise party - now that's friendship! However, the time and energy (and consideration) that he has for his friends just goes downhill as the show goes on. It may not be unrealistic to have a man basically start ditching his friends once he gets married and has kids, but that doesn't make it ok.
We Know, You're An Astronaut
Howard managed to become an actual astronaut, after his work in engineering sent him into space (despite being completely physically unprepared, in terms of size and fitness). It's an amazing achievement, and while it was a bit of an out-there storyline for the show, it generally worked.
However, once he came back to Earth, he drove everyone nuts with his constant boasting about it. Given that he is friends with eventual Nobel Prize winners and general overachievers, it's not actually that huge a deal in his social circle... and there's certainly no reason to get this annoying about it.
The Way He Treats Stuart
Overall, the way that the show treats poor Stuart just gets worse and worse as the seasons pass, but Howard is certainly more guilty of this than most. At the start of the show, Stuart is the owner of the comic book store, a great artist, and actually a bit more socially capable than many of the gang. By the end, he's a parody of a sad sack, which is a shame. And how Howard treats him changes too - he essentially becomes an emotional punching bag for Howard, who then lets him move in but holds it over his head, uses him as a babysitter, and makes fun of him constantly.
His Relationship With His Mother
It's a running joke at first - that Howard hates his wildly overprotective mother, and that they are constantly yelling at each other across the house. As the show goes on, though, things get worse and worse. His mom becomes not just overprotective, but fat, ugly, annoying, etc. He starts yelling more and more, treating her more and more badly, and by the time she passes, it's just sad to see him lose any opportunity to repair that relationship.
Shameless About His Abandonment
Speaking of sad - when Howard first reveals how his father ran out on him as a kid, and all the ways that he has been searching for his father's love since then, it's a sad story. However, as the show goes on, fans feel less and less sorry for him, because this goes from something that he acknowledges to being something that he actively uses to try and get people to feel bad for him, to try and manipulate them, and generally to make the world throw him a pity party. It's not a good look.
How He Behaves In Texas
Sheldon's mother is a fantastic character on the show - the uber-Christian mother of an atheist genius, who still manages to accept and love everything about him and his friends. She is wonderful to everyone, and the majority of the gang appreciate her and look forward to her visits... however, Howard, who usually seems to like her, behaves appallingly in Texas.
He and Raj head down there to visit, and Howard dresses up like a cowboy and puts on a Southern drawl... a disgustingly rude parody of a culture to make fun of a woman who has been nothing but kind to him.
Never Really Grows Up
Throughout the show, most of the characters do at least some 'growing up', whether that is conquering fears (like Raj), learning to love (like Sheldon), or gaining some confidence (like Leonard), but Howard seems to grow up the least of them all. Sure, he gets married, he becomes a father, but in terms of real character development, there's very little. Of course, technically this isn't something he does that makes him a worse character - it's what he doesn't do, and that's grow up.
His Sitcom Husband Antics
This is linked to the previous point, but Howard starts out as a good friend... and ends up as a bad husband. In many ways, he feeds into the worst sitcom husband stereotypes - becoming the 'fun' one, while his wife has to do all the housework, cleaning, and organizing (or trick Raj into doing it for her). There are plenty of moments where he becomes the lazy guy ignoring the work that needs to get done, and it's a boring storyline for yet another sitcom husband.
Not The Best Parent
He's also not a great parent, which is a shame for a character whose relationship with parenting is probably most explored of the main characters on the show. He loves his children, of course, but he doesn't want to show weakness in front of them, and fights Bernadette on having a bedtime story published because he needs to be seen as a 'strong man'. And, of course, there are plenty of 'jokes' about Bernadette (or Raj, or Stuart) doing the lion's share of the work, while Howard just sits around making obnoxious jokes.