What others have said pretty much. Don't let mean comments get to you.
i.e something like "your comic sucks brah. Kill yourself!" is probably some asshole kid (or worse, person your age) trying to get a rise out of you. This is commonly known as "trolling" here on the internet. If there is one piece of advice I can give you, it is this.
DO
NOT
FEED
THE
TROLL(S)
!!!
The more you or others engage with one, the more it will harass you and sometimes everyone else. The best thing you can do is block/report these kinds of people and move on hoping it will get tired and find something else to do.
As for your comic itself, while you should listen to somebody who actually has something of value to say regarding the overall quality of your webcomic, you can likewise ignore people who give you "constructive criticism" in the rudest way possible. Bonus points if they compare your craft to theirs while giving you an unnecessary roast. I had this happen to me on DeviantArt once. Yeah...nuff said.
(Hint: Anybody who does this is certainly NOT better than the person they claim to be better than.)