Expanding or diminishing proportions can be a fun way to create humor in a public speaking engagement. It's similar to a caricature artist that outrageously exaggerates the features of an individual, while still keeping the person recognizable.
I did a public speaking engagement one time for Secretaries Day at a large insurance company. I was making a point about how hectic it always was for the secretaries. It went like this, 'You're answering the telephone, the fax machine is ringing, you're making copies, and you're filing every policy clear back to 1910.' The secretaries could relate to each item mentioned. They obviously did lots of filing, but certainly not as far back as 1910. Exaggerating this date was funny to them and drove home the point that they always had lots of work piled up.
The key to using exaggeration is to inflate or deflate whatever you are talking about so much that it is obviously an exaggeration. In the last example you wouldn't want to use the year 1999 if you were doing the talk in 2000 because it is very likely that an insurance company would really be working on a file for a year or more. That's not funny.
Of course, who am I to tell you what is funny. I spent two terms in the third grade . . . Truman's and Eisenhower's. hahahahahahaa