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
Example Conversation on the BBS (sarcasm version)
She’s so cute, check it this!
>>55 >>56 Same ID, sock puppet otsu!
>>55 >>56 IDいっしょじゃねーか、自演乙