I understand most of the following story, except for the highlighted part:
Berkenalan: Pada salah satu pelabuhan laut di Tanah Papua, sedang berbincang tiga orang pria yang sedang menunggu datangnya kapal penumpang, untuk menjemput sanak familinya. Ketiga pria tersebut berasal dari daerah yang berbeda, antara lain dari Ambon, Batak dan Manado.
Sebelum perbincangan dimulai, ketiganya memperkenalkan diri masing-masing, maklum baru saja kenal, sambil bersalaman. Pria yang dari Ambon memperkenalkan dirinya kepada pria yang asal Batak : "Bakarbessy," sambil jabat tangan. Pria Batak menjawab sambil jabat tangan pula dengan menyebut dirinya : "Batubara.".
Pria yang asal Manado ini sambil kebingungan melihat kiri dan kanan, setelah mendengar kedua rekannya tadi masing-masing menyebut barang panas. Tanpa berpikir banyak pria Manado tadi sambil jabat tangan mengucapkan "Air Mandidi."
I am also a bit confused by the joke. I know "bakarbessy" and "batubara" involve fire and coal, but why did the third man respond "air mandidi"?
1. "Maklum" according to the KBBI means paham or mengerti (to understand). In this case, the sentence "maklum baru saja kenal..." kinda means "because they just met/knew each other" or more literally or perhaps roughly translated : "it's understandable that that they just met, so they did a handshake".
2. As a start, "Bakarbessy" and "Batubara" are actually last names that are common in these tribes/regions (Ambon and Batak). This Manado person (assuming that he didn't know the actual meaning of those words) thought that the words translate to something hot or heated, which is the literal translation (fire and coal are somehow hot, right?). That's why he replied with "Air Mandidi" which translates to "Boiling Water" in Manado-nese ("Mandidi" = Mendidih = to Boil) and the supposedly funny part of the story is I've never heard Air Mandidi being used as a last name.
CMIIW :)
"maklum" is an informal Indonesian word from "tetapi". It is typically as a slang because you cannot use it in different types of sentences.
"baru saja kenal" phrase, you can say as "we just meet/know recently."
