When crafting your subject lines, you have to consider how your audience will perceive it, especially if you want to get 'cute' with it. And be sure to follow up right away in the message...
This morning I received an email from a retailers in which I immediately noticed something odd in the subject line. First a little background... In Canada, we have a long weekend in May around Queen Victoria Day (May 24). This weekend also usually means the start of hot summer weather after a cold and dreary winter. So naturally, it usually means packing up and heading to the cottage or camping to drink a few cold ones. Therefore this weekend is commonly referred to as "May 2-4 Weekend"
There's really no mention of any sale or promotion, except for the 35% off circle, which has nothing to do with 2-for-anything. It's not until I scrolled down to see the "2-for-$100" text at the very bottom of the email.
I guess this is more of an above-the-fold lesson--but if you're going to use a clever play on words in the subject line, make it obvious right away when the email is opened!