Many people who think of spam tend to think of them as worthless mass of emails that can cause no damage or harm in looking at them. This view, however, is wrong. Some spam messages are capable of immediately installing harmful malware that can seriously harm the function of your computer. In some cases, they could even make your software completely unusable. The following post from Jatheon.com gives you a fair amount of insight into the dangers of spam. http://jatheon.com/the-dangers-of-spam/
Some messages are harmless indeed and could provide a fair chuckle if they were to be looked at. Despite the harmlessness of them, it is better to just not take the risk of any possible malware and avoid opening the message all together.