Someone, usually a male around his teenage years who pretends to be funny. He uses mostly slapstick humor (usually involving the removal of his own clothing or the putting on of woman's clothing), corny old jokes or in general just acts like a three year old.
As a former cheeseball myself I can attest that most cheeseballs use this humor to try to get cheap laughs out of people in hope that they will like them more. 99% of the time the cheeseball just looks like a jackass however that 1% the cheeseball miraculously goes about making friends.
"Look at me Lila I'm a Viking!" as this particular cheeseball blocks the path of his girlfriend in an aisle while wearing Viking horns.
"I can speak bird - 'meow, meow'" - said as someone points at a pidgeon in a park.
Guy A: Wow you like men
Guy B: No you like men
Guy A: No she likes men (pointing at a girl)
Guy B: Haha girls like men! (Both in this case were cheeseballs)