A euphemism for I don't give a shit. Especially useful in response to unsolicited bragging or otherwise useless information. Stems from Costanza in The Opposite episode of Seinfeld.

Seinfeld: Chicken salad's not the opposite of tuna. Salmon's the opposite of tuna. Cause salmon swims against the current and the tuna swims with it.

Costanza: "Good for the tuna."
douche: "I worked really hard this weekend, but it payed off -- my boss said I did a great job!!"

dude: "Good for the tuna"
by ChrisGGG November 7, 2010
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A metaphor to describe the quality or enjoyment of sexual activities with female, almost always but not necessarily involving the vagina.

Alternatively can be used to explain the pleasure of a meal.

*note: tuna can be changed to pork if describing sexual contact with a male.
Example 1:

Friend: Did you pull last night?
You: Yeah man!
Friend: How was it?
You: Let's just say it was good tuna

Example 2:
*During intercourse with a female*
Internally to self: Oh yeah, that's good tuna.
by definitelythatguy April 7, 2018
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