Good morning. I am a fool.
ohayou(おはよう) - not ohaiyo = good morning
watashi(私) = I
baka(ばか) = a fool
Watashi Wa Baka Desu
The other answers say it means 'you are stupid', so I'll say why it made you sound young. Anata is the "default" form of you, the kind you learn in school but very rarely use in real life (because subjects are dropped a lot, mostly). It's pretty formal, so it's like saying "you, my good sir, are a dummy-head." It makes you sound dumb yourself. Definitely keep in mind some regions don't find it that bad a word and some other regions consider it really really bad! Also, an extra note about one of the other answers below saying that you should switch to anta in less formal situations; anta also implies closeness (like with your girlfriend or best friend) so using it to insult a guy on the internet makes you sound creepy, too. Japanese is pretty hard to sound intelligent in, sometimes.
Actually it means someone doesn't know much about Japanese.
ohaiyou means good morning. it is a form of the adjective that fits with the respectful ending gozaimasu. (ohayou gozaimasu.)
watashi wa baka desu means I am a fool.
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Anata = You wa = are baka = idiot, stupid You are stupid, You are an idiot, etc. He was patronizing you for acting like you speak Japanese.
soph is right...
trust him... his source is 'mother tongue'
i dunno what kind of a source that is... but it sounds epic...
u dont mess with mother tongue...
but fool sounds so lame and old fashioned... i go with idiot...
its more 'hip' with the kids these days... trust me... i am one... o wait... no wait... i shoulda written that in my source bit... ill do that...
even though its nothing compared to mother tongue..
"hello, i am an idiot"
Hello, my name is Idiot
no joke, thats what it means