The idea itself while sophomoric is still humorous, so that's covered. Anything involving a great deal of pain without permanently injuring the character is always funny (re: slapstick) so just showing that alone would be funny to a lot of people. Let's say the character has to explain what's happening to a friend over the telephone, or is in the other room, then he has to describe the situation. As it reads above, he states exactly what's going on, a small animal is chewing on his testicles. How can this be improved?
The English language is handy in that there are more words than any other language and it's easy to make up new ones, invent slang, and misconstrue the meaning of other words (which is also slang, but go with it) for a situation. There are also words that make people smile. Just a certain way that they sound that brings out the comedy. It's been said by many people that anything with a "k" is funny. I tend to agree simply because "k" is a funny sound. Pickle. Say it out loud. Then say it out loud three times really fast. Whee! Of course don't limit yourself to talking about the Ku Klux Klan molesting a duck simply to cash in on an idea, I'm just saying a "k" word here and there never hurt.
So let's look at the first part of our sentence "a small animal." There are a lot of small animals in the world, so let's think of some funny ones. If we want to go with "k" we could say muskrat or skunk. I, personally, think a weasel is the funniest sounding animal. If we want to throw a "k" in there as well, we can call it a stink weasel. So our sentence has transformed into "There's a stink weasel chewing on my testicles!"
On to our verb, "chewing." This is where a thesaurus comes in handy, there are a lot of ways to convey that something is chewing, so let's look through the list until we find a word that just seems silly. Here's what we have: bite, champ, chaw, chomp, consume, crush, cud, deliberate, eat, gnaw, grind, insalivate, manducate, masticate, mull, munch, nibble, ponder, ruminate. There are more, but let's look at these. We don't want to use a word that not many people would understand or anything too outdated. The word should also sound painful while still being inherently silly. To narrow it down, we can use "gnaw" or "nibble." In my own personal opinion things with two unconventional letters in a word usually wins, but in this case I like the idea of gnawing. The idea of a stink weasel either gnawing (just going balls out) or nibbling (saving the delectable feast) on testicles is pretty funny either way, but I'm just a fan of the gnaw. Our sentence is now "There's a stink weasel gnawing on my testicles."
We're now down to the "testicles" part of the sentence. While descriptive, the word testicles is both a mouthful and not that funny. Here's where we can use some tried and true slang or just make up our own. As long as the audience is seeing what's happening we can get away with just about anything. People have some interesting pet names for their balls. At any rate, just for a sampling, let's go to the urban dictionary and see what we've got. So under "testicles" we've got: balls, nuts, scrotum, sack, testes, bollocks, gonads, nutsack, nads, vagina, ballsack, sac, genitals, family jewels, teabag, junk, nut, chode, jewels, bag, nards, rocks, berries and grundle. All of those are fine, but we should make up our own slang word here. If you know your character well, just think of what they would call it and go from there, but in this case I'll just make something up (and remove "on" from the sentence). Our sentence is now, "There's a stink weasel gnawing my happy sack!"
Not the best, but hey, I'm making this up as I go along. It sounds a little close to "hackey sack" but we'll just go with it. So our sentence has gone from "There's a stink weasel biting my testicles." to "There's a stink weasel gnawing my happy sack!"
A vast improvement? Not really. A decent improvement - yes. With this line our scene is halfway there, especially if the visual is spot on. In order to make this a complete comedy exchange, the reply to this line has to be unexpected, that's where people will laugh. Let's look over the scene now.
Chip is walking through the park arguing with his girlfriend Kandy (stripper name?) on his cell phone about her jacking a guy off in exchange for a meatball sub. Then, in the midst of the argument, a small animal darts out of a nearby bush, runs up Chip's pant leg and goes right for his nuts, and he lets out a scream.
CHIP
"There's a stink weasel gnawing my happy sack!"
KANDY
It's always you, you, you.
There are a million unexpected replies to this. That's what makes a comedy fun, make your characters not care about each other and see where it takes you. In retrospect this was kind of a dippy example, but using funny words will get your that much farther.
