I just think it shows a lack of creativity and appreciation. If something cracks you up so much, at least take a second or two to acknowledge with words the efforts of the person who, for a brief and shining moment, brightened your day with humor.
And the odds are? Unless you are a total dipshit with zero self control? You are not, in fact, chortling audibly for any passerby to hear. And, to take it to the next level, you have also probably not dropped to the floor while chortling audibly and begun to gyrate to the point that your buttocks detach from your body.