It seems some people didn't bother watch a Leaf game last year. Boring team? The Leafs were far from boring. They may not win very much but to call them boring is ignorant. Anybody who finds the Leafs boring needs to check out some of the other teams around the NHL. Teams like Boston just sat there and trapped the entire season, something the Leafs never did.
Anyway drifting back on topic, the Leafs are hated for so many reasons and it goes beyond hockey.
First and foremost, let's set aside the "their bad" argument because nobody really hates some other teams that haven't been successful post-lockout. See: Atlanta, Florida, etc. To take it a step further, let's set aside the "No cups in 43 years" argument as well as you don't see St. Louis and Los Angeles hated nearly as much as the Leafs. The bottomline for that is that people really don't care how poorly a team does on the ice unless its a rival or a 2nd favorite or what not.
What people do seem to find annoying is that the Leafs are still "relevant." Oh look, the haters are licking their chops to get a chance to say "The Leafs aren't relevant! their bad!" Guess what guys, they are. Despite the inepitude, every hockey board including this one has a new Leaf topic daily. When 7th defensemen like Brett Ledba are signed, they instantly become the "Trending" topic on Twitter. Some say its jealousy that the Leafs can still be so popular while other franchises in the same position become practically irrelavent to the hockey world. Personally? I think people just get sick of hearing about the franchise.
Pushing it further, Leaf fans seem to be endlessly optomistic. Every year is a chance for the playoffs or the cup, no matter how poor the team played the year before. Eventually, people tire of that too. They tire of the overrating of players, they tire of a franchise that finishes 29th place and yet still can't seem to do any wrong. The Leafs also have a greater concentration of fans then most teams which leads to more less versed fans.
Finally; the media. The Leafs are the front page news. Every national newspaper is Leafs first, every news network is Leafs first, every sports channel (See:TSN and HNIC) is Leafs first. You could understand people would feel their team is not getting enough attention, given this situation.
Taking the hate outside of hockey, many Canadians outside of the Greater Toronto Area hate the city of Toronto themselves. They claim everything stupid from the city being too "American" to the city being the attention of attention in the country's media to it being extremely dangerous (Hence the nickname "Trauma", Ironically the city is the safest of the "Big 6" in Canada and is safer then the majority of US cities as well).Don't believe this hate exists? CBC actually made a comedic movie about it if your interested. It's called "Let's all hate Toronto."