This exercise is specifically designed for when you are sitting in a tight space, like on flight sitting economy. Sit up tall on the edge of your chair. Reach your arms straight out in front of you and place your hands on either side of the seat in front of you (roughly shoulder height). You may need to slightly bend your elbows so as not to grab the head of the person in front of you! Gently, start to drive your arms towards each other as if you were going to crush the chair in front of you. You should feel your chest muscles and arm muscles tightening up. Focus on those muscles tightening up. Hold for 8 seconds. Relax for 8 seconds and repeat. Try doing this 8 to 12 times.
SPECIAL NOTE: For all the In the Gym: Cable and Dumbbell exercises pick a weight that you can do for 8 to 12 reps fairly comfortably and with perfect technique. After a couple of weeks of performing at this weight and with perfection, on then, move up to a slightly heavier weight that feels challenging once you get to that 8th or 12th rep. Once you feel absolutely confident in performing every rep with absolute perfection, only then, go to a heavier weight that is challenging you through out the set.