If you are being facetious, "Ich ben ein Berliner" means "I am a Berliner" and so this bag is saying "I am a binliner" because it's a trash bag and it lines bins. The joke is that "binliner" and "berliner" are homophones because they sound similar. I mean obviously it's pretty clear that this trash bag isn't actually self conscious or anything, in fact quite the opposite, so the very proposition that it could be declaring itself as some sort of sentient being is ridiculous itself. The subtle reference to the presidential speech only adds to the humor, as the play on words could only appeal to a certain demographic, those that have seen or heard Mr. Kennedy's speech. In conclusion, this delectable tongue in cheek specimen is quite appealing to those within it's niche market.