Persuading investors or partners to take a chance on your new idea can be a bit of a challenge. With so much competition, so many variables, and a very short window of time to "impress" - you might wonder why entrepreneurism isn't an Olympic sport.

This is where a special brand of passion comes into play. Sure, sometimes you go into a traditional meeting and eventually win. But other times call for a bit more creativity.

Here are some hilarious "defining moments" from some of your favorite startups!

1. Selling Cereal

During the 2008 election, Airbnb co-founders Brian Chesky and Joe Gebbia were looking for smart ways to raise capital, while avoiding common small-business financing mistakes. Naturally, they decided to design cereal boxes that made fun of the candidates and sell them at convention parties!

Chesky and Gebbia sold 500 boxes of Cap'n McCain's and Obama O's, which raised a cool $30,000 for their company (which then was called Airbed & Breakfast). The money didn't last long. However, their luck changed when they won $20,000 by joining Y Combinator and subsequently secured $600,000 in additional seed capital from Sequoia and Y Ventures. In 2015, Airbnb expects to collect $675 million in revenue and is valued at over $20 billion in the venture market. Goes to show that you should never give up (and always eat your cereal).

2. Sealing the Deal in the Gym Locker Room

When you're nervous, they say to imagine the audience in their underwear. This particular story brings that to life in a very real way!

Coming up with a great elevator pitch is no easy feat. Plus you have to be ready to launch into it at any time. 6sense founder Amanda Kahlow delivered hers when the woman she'd seen at the gym every day turned out to be (that's right) Lynn Vojvodich, CMO of Salesforce.

Kahlow had courted Salesforce as an investor, but the deal was awaiting approval by Salesforce's top marketing executive. The same executive who went to the gym at 6 a.m. every day, just like Kahlow did.

One pivotal day, during a casual conversation about grapefruit-scented lotion, Vojvodich mentioned she worked for Salesforce. Kahlow mentioned the potential investment in 6sense, and Vojvodich revealed that she'd been asked to be its executive sponsor. She asked Kahlow for her elevator pitch, right then and there, which Kahlow delivered while wearing only her underwear.

Salesforce signed off on the investment, and Kahlow sent Vojvodich some grapefruit-scented lotions as a way of saying "thank you."

3. Apologizing for Being Late...With Beer

Grocery delivery service Instacart stakes its reputation on being prompt. The company delivers groceries in 12 cities, with delivery times as short as 12 minutes.

The punctuality for which Instacart is known, however, didn't apply in its earliest days. CEO Apoorva Mehta missed his initial Y Combinator deadline by two months, but he didn't give up on getting his shot.

Mehta sent YC co-founder Garry Tan a six-pack of beer, delivered by Instacart, along with a plea to let him into the program. Within a half hour, Tan called Mehta back and invited him to YC headquarters to meet its partners. Never underestimate the power of beer.

Sometimes, founding a start-up means you have to be bold and grab an opportunity when it comes. Any moment might be your defining moment...forewarned is forearmed!