it's sometimes accompanied with a ;).. BUT it should be read with a sarcastic undertone if the ;) has been added.
It can be interpreted wrong, be careful with how you use this! To avoid misinterpretation, add the ;)
friend nr 2: *thinking I dont want to do this, putting on the fake happy voice* "yeah sure, it's a date ;)
"Wanna go to the library and do some serious studying?"
"Yeah, it's a date!
John: Sure, how about a blow job?
Female officer: OK, pull around to the corner.
3 seconds later...
Female officer to cop in van: "it's a date"