Meaning of “Otsu(おつ / 乙)”
Basically, It means “Thank you for your hard work.” or “You did a great job.”.
“Otsu(おつ)” is an abbreviation for “Otsukaresama(お疲れ様)” and this is a slang.
Otsu(おつ) have two meanings.
One means “Thank you for your hard work”.
We use “Otsu” when we want to thank someone for his/her great work.
(This is a slang so it’s too frank to use against elderly people)
The other means “Thank you for your ‘stupid’ work”.
In this case, “Otsu” is a sarcasm.
Example Conversation with a friend
[They are playing a online video game]A: It’s time to go
B: Otsu
A: そろそろ落ちるわー
B: おつー
Example Conversation on the BBS (sarcasm version)
55[ID:000001234]:
She’s so cute, check it this!
56[ID:000001234]:
True!
57[ID:xxxhoge]:
>>55 >>56 Same ID, sock puppet otsu!
55[ID:000001234]:
この子めっちゃ可愛いから見てみて！
56[ID:000001234]:
ほんとだ！
57[ID:xxxhoge]:
>>55 >>56 IDいっしょじゃねーか、自演乙
If I understand the example correctly, xxxhoge is saying “thanks for your work /s” to 1234, right?
xxxhoge is saying to 1234, “Thanks for your work
(I know you are the “she”, you are praising yourself while pretending to be someone else)” with a touch of sarcasm.