Variation on the more commonly accepted and widely practiced self gratification pastime, masturbation. Could be Italian in origin.

According to Ste Roberts, the method involved boiling an amount of pasta (pasta type was not specified so presumably most shapes will suffice)until 'al dente', then transferring pasta to an empty jam jar, leaving the lid off but covering the top with a double layer of cling film into which a small slit is made.

Once pasta cools from very hot to quite warm, the pastabater's penis can be inserted into the jar of pasta, at which point the pastabating can begin in earnest.

Never actually tried this, however having actually written the process up, it sounds more plausible than it did 20 years ago.