Tell a joke or leave. You are about to have one of those 'difficult conversations' with someone at work or a loved one. You'll get an attitude adjustment that will positively adjust the outcome of your conversation. You are about to go on a job interview. If you really want the job, go to the rest room to primp and to work up a great big belly laugh.
Studies show employers choose vital, enthusiastic candidates over sullen, serious ones.
You are exhausted. It is the end of the day. You have worked, helped others, and performed the daily rituals of living. Now do something for yourself, something that will make you smile in celebration of you. Smiles are the external expression of an inner titter.