Maybe the agent you messaged knows it, but even if he does, the others might not. Do yourself a favor and use the ever powerful emoticon, unless you don't really care that most everyone thinks you are a jerk.
"You suck dude." Could be fighting words, but "You suck dude. :-)" doesn't sound so much like there are tears dripping onto your screen.
And hey, now you can rise above it. Just point those rude folks here for some lessons in class like Ramb3er did!
I guess our fine green friend didn't realize Rambl3r was giving him a tip!