by Elvis Presley.
Always makes me happy.
According to wikipedia, occasionally during live performances Elvis would randomly change lyrics to give them humorous connotations. In this version, recorded at the International Hotel in Vegas on August 26, 1969, instead of singing: "Do you gaze at your doorstep and picture me there", he sings "Do you gaze at your bald head and wish you had hair" (0:42 in the video). Apparently at that point he saw a bald man in the audience.
From that point on Elvis can't stop laughing. Pure and honest laughter.
As a bonus check out the second video, showing Elvis singing the same song - only this time instead of changing the lyrics to something funny, he just babbles. This performance is from 1977.