My favorite's pretty rare, but it's gotta be ぷくぷくした. ぷくぷく is the sound of bubbles or 'blup-blup', and if a soft drink bubbles over or something you can say, あ、ぷくぷくした! It's more popularly pronounced ぶくぶく because it's a bit hard to say, but that takes the fun out of the whole thing.
The reason it's funny is primarily because of devoicing rules. Let's review (sorry, but this is easier to write out in romaji): In standard Japanese any unstressed 'u' or 'i' sound that is between two consonants which you don't pronounce with your vocal chords, you cut off your vocal chords and only 'whisper' the vowel. The consonants for this are K, T, P, H, S. So for these situations
(K/T/P/H/S)//(U/I)//(K/T/P/H/S/silence)
you don't pronounce the 'u' or the 'i' in the middle.
So when you say ぷくぷくした it's all devoiced except the 'a' sound at the end: p(u)k(u)p(u)k(u)sh(i)ta or (roughly) pkpkshta.
Neither ぷくぷく nor ぶくぶく seem to be in rikaichan or wakan (except the latter with a different meaning), but surprisingly they're in my electronic dictionary.
Last edited by Tzadeck (2009 August 30, 8:59 am)