Photobomb - As in I'm getting ready to take a photo and someone runs into the background doing something stupid and screams, "photobomb." This is an act that could eventually incite a homicidal rage.
Hashtag - Hashtags don't necessarily annoy me. What irritates me is when people say the term "hashtag" with the phrase. For example, "My manager at work told me I couldn't take off this weekend for the One Direction concert. Hashtag so lame."
Meh - "How are you doing today?"
This is not an appropriate answer.
YOLO - (You Only Live Once) Do I really need to explain this one. Why is this the new mantra for today's youth? Just wait... this will replace "Hey, watch this" as famous last words before people make stupid mistakes. I can see now some idiot letting a buddy make them a homemade suit and attempting to base jump off a cliff, screaming, "YOLO!!!!!" on the way down.
SMEXI - a blend of the words smart and sexy. Which you are neither in my opinion if you use the word SMEXI.