Buen Humor

Buen Humor
 

Hello All!
I've read the following joke in an old Spanish weekly called Buen Humor:

- Te digo que no voy a tres-prima ni cruzo siquiera el Adriático.

- Me extraña; porque tu hijo mayor dos-prima bastante bien.

- Yo mismo dos-prima-dos siempre más que él; pero no me decido.

- ¡Vamos, que tú, sin viento todo, no te atreves!

but I can´t figure out what is the exchange and why it should be humorous. Could anyone help?

Thanks,
Gedeon

Without any further context, I suppose one would have had to guess the meaning of "dos/tres-prima" from the same pages in the magazine to know what the joke is about.