Just.No.

Scenario 1: You're on a dating website and you have been exchanging messages with an attractive woman who you strongly believe is interested in seeing your penis. She hasn't exactly come right out and asked you about your penis, but you're pretty sure she wants to see it. Like, 60% sure. Also, you're drunk.
Should you send the lady a dick pic? No.

Scenario 2: You have this hot friend with whom you would not mind having sex. She's single and earlier in the evening you flirted via text message. She just sent you a winky emoticon, which everyone knows is code for "LET'S DO IT." I mean, she didn't expressly ask for a picture of your junk, but she must want it, right?
Should you send the lady a dick pic? No.

Scenario 3: You've been going out with a woman for a few weeks, so it's still in the fun stage before you've noticed how much you irritate each other. The sex is fun, and frequent, and great. You're spending a night apart; she's out with her friends. But you want her to know you're thinking about her in a sexy context.
Should you send the lady a dick pic? No.

Scenario 4: You're so mad at your ex girlfriend and you want to remind her that there's no possible way her new boyfriend's penis could measure up to your penis, which is great. Also, you're drunk. You're so, so drunk.
Should you send this lady a dick pic? God, seriously? No.

Scenario 5: You're flirting with this person who you follow on Twitter. It's gotten past the DM stage and you've exchanged phone numbers. You want to break the ice while making it clear that you, Captain Thundercock, will not be friend zoned.
Should you send the lady a dick pic? No.

Scenario 6: One of your female friends/your frat brother's girlfriend/your friend's sister is a total prude who needs to loosen up.
Should you send the lady a dick pic? No.

Scenario 7: You are a Musician and your ambitious, beautiful, and pregnant wife is never around and she's like no fun at all and you just want to feel LOVED and ADORED and your ego is hungry, hungry for approval. Tons of hot chicks follow you on Twitter and Facebook, because you are a Famous Musician, and you just know they want to see your junk. Your perfect, talented junk.
Should you send the lady a dick pic? No, you fucking creepy dumbass. No you should not.

Scenario 8: You know for a fact that the woman in question would like a picture of your penis because she specifically asked you for one.
Should you send the lady a dick pic? Is there any possibility whatsoever that one day that dick pic might be used to publicly embarrass you? If yes, then no.

There you have it, men —  Happy sexting.