It is important to be authentic - to be yourself - when working with students. Students have an uncanny ability to see through someone who is putting on an act.

This being said, there are times when it is appropriate to be funny and times when it is inappropriate. In the Bible, the book of Ecclesiastes, Chapter 3, we find that Solomon wrote about there being appropriate times for everything... "A time to cry and a time to laugh. A time to mourn and a time to dance..."
I'm sure that in addition to the naturally funny side of your personality, there are other parts of your personality. No one is "one-dimensional." Even how you word your question shows me that you have a caring, sensitive side.

While you may be known for your sense of humor, I'm sure that the students who know you best, know that you are more than just "funny". I think that you have to make an intentional decision that you are going to act in appropriate ways - whatever the situation calls for. For instance, you may be tempted to say something funny when a student shares a problem with you. Think before you speak. Remember that the Bible says, "Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen." Ephesians 4:29.

http://www.simplyyouthministry.com/community-articles-jim-s-thoughts.html