NCIS riddle

Question: a man walks into a bar and asks for a glass of water' the bartender pulls out a shotgun and shoots missing the mans head by 2 inches. the man stands up lays a 20$ on the table and thanks the bartender. why did he thank the bartender?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: During what month do people sleep the least?

Question: When is 99 more than 100?

Question: What can be broken but never forgotten?

Question: Surrounded by life , yet life is its biggest enemy. But without life there is no need for it to exist. What is it?