The joke: “So there’s two people on a boat. And they have three cigarettes, but they don’t have a lighter, or any way to light them, right? So one of them looks to the other and is like ‘What do we do? There’s three cigarettes?’ So the other one takes one and throws it overboard. And the guy’s like ‘Why’d you do that, you just threw away one of our cigarettes.’ And he’s like, ‘Well now isn’t our whole boat a cigarette lighter?’”
The informant heard this joke when a friend texted it to him; presumably the friend got it from either another friend or online. The joke deals with a pun, and the clever use of wordplay. It’s kind of anti-funny, but just enough to get some laughs when the audience figures out and understands it, which is why I imagine people tell it. It took me a few seconds to get it myself.