I kind of think it's hilarious, and that Tosh.0 has crude but funny humor.
Like seriously guys, if you were to say our fanbase is completely normal you'd have a huge lie.
In my opinion there are 3 stages to the MLP fandom - the casual watcher - where I would group myself - includes just enjoying the cartoon and participating in minimal fandom events. There is the Brony, which is the more engaged viewer that participates in fandom events such as fanfictions and Brony music. Lastly there is the Clopper part of the fanbase, where people are sexually enthralled with the cartoon. I can't say there is anything wrong with those sorts of mindsets... people will like what they will.
Unfortunately for the fanbase, cloppers are generally regarded as "unsavory" to say the least. Fandoms are judged on their worst and weirdest, and for the MLP fandom it happens to be cloppers. While I know that humans will sexualize basically anything, and that it is completely normal to do so, people can't help but laugh at those who enjoy the more adult side of this fanbase. And I can't blame them either... it would seem pretty fucking weird, eh?
So just move on and understand, stop giving Tosh flak if you hate him (he just gets more views) and learn to laugh at yourself. We're weird.
Bronies are weird.