ive only recently (last week) started vlogs myself... so havent attracted Trolls yet ..  :roll: 
generally though .. from watching YT vids over the years .. ignore the trolls... dont engage them with comments if you can manage it!
usually if someone does a blatant troll and is being an ass-hat along with it .. the other users of YT that view it .. will start to vote it down, it gets removed from view... apparently you can still look it up if thats really what you want to do... 
Do Not Feed The Trolls .. is probably the best thing  
 
 
they thrive on creating drama and arguments and making people aggro .. so just leave it be?
so many viewers and uploaders get bent out of shape so easily now... the social media phenomenon has made it simple to have an argument with the whole world! .. just because anyone put a Video or comment up does not mean or guarantee that everyone will love it! 
if you really dont like the troll (maybe you know them ..or have commented on their stuff so... now they are 'getting you back') .. and you find their comments personally distateful... then there is no real limit.. just block them and be done with it! .. no point in getting stressed or annoyed by having to wait till the troll 'crosses the final line' .. 
We all have our Trollish moments... you either have to just block them .. or tolerate them ... there will always be more viewers and more trolls... guaranteed!