Lovely Complex is about a girl called Risa, and she's exceptionally tall for a Japanese girl. The second main character is a boy, Otani, he's exceptionally short for a Japanese boy. When people see them together, they are reminded of a comedic duo in Japan which has 1 tall member, and 1 short member. Because of this comparison, Risa gets mad and yells insults at Otani. Otani being as stubborn as Risa, yells insults back.
That's how they became friends. Risa and Otani are surprisingly suitable for each other, having friendly arguments constantly, and otherwise sharing their hobbies together. Aside from the insults to their heights, a real complex about their height issue is almost never touched upon. Maybe twice or something. Lovely Complex mainly deals with the budding friendship between Risa and Otani, and their constant arguments (but it's definitely not a love-hate relationship), while sometimes bringing in secondary characters to propel the storyline forwards.
Personally, to me, Lovely Complex is the best manga when it comes to realistically portraying a high school romance. Risa and Otani start out as friends, they don't suddenly start crushing on each other. The longer they are friends, the more Risa starts to like him, until eventually she does.
But get this - Otani isn't quite there yet and still likes her as only a friend.
I have never read a manga that did that, and I'm pleasantly surprised how Lovely Complex deals with this issue, it feels so realistic.
Aside from the realistic portrayal of the character's feelings, Lovely Complex is downright funny. There's some nice jokes here and there, and some that will crack you up. I personally find Risa's 'ugly' faces hilarious, and it really adds to the humor.
I'm so glad that Risa isn't one of those generic shoujo girls who cry in every chapter and when they're about to get raped by gangmembers, the Jerk With A Heart Of Gold comes and saves her. Risa is spunky and funny, and none of those things happen in Lovely Complex (except for the crying part, which is completely acceptable when it happens), and Otani isn't the jerk with a heart of gold. Sure they constantly bicker, but never once has Otani said he hates Risa, he's always shown as having great fun with her.
I adore Lovely Complex, I really do. The perfect mixture of realistic romance and comedy, it's just an overall awesome story to read. Try and watch the anime if you can as well, since it sticks close to the manga, seeing those funny moments in action is double the fun.