It's wrong to make up a story.
Dave comes back from vacation and sees his friend Mark who asks him what he did while on vacation.
Dave wants to answer Mark's question.
Dave tells Mark that he did a lot of swimming and tanning and that it was a low key vacation with nothing particularly exciting happening.
Dave tells Mark that he fought a great white shark while swimming and that he managed to subdue it while underwater.
Mark is happy to hear his friend had a relaxing time and got to spend time in the sun.
Mark finds that story hard to believe and feels weird about being near Dave and wants to leave.