Well this question grabbed my attention and hence I thought of answering it. Given below are the few things that I do when no body is watching me. I am not sure where they qualify being weird or not.That's for the readers to decide.
1) Reading out loud and recording it in my phone : I read out few passages from a novel out loud and record it. People say I have got a mixed accent. So sometimes I try pronouncing words in different ways.It's like experimenting. Later I hear those recordings and try to realize which words sound better in which accent.
2)Jumping on the bed : I don't know how to dance. Hence jumping on the bed seems like a great idea. I don't turn on music player (R & B music) and shoot up the volume of the speakers...I don't want to grab anybody's attention right.? My ipod comes to my rescue . (It's pretty difficult to jump while using a cell phone to listen to music :( )
3)Watching how dawn turns into day: I tried this few times. I had set alarm for 3 am . I woke up with sleepy eyes and opened my window to observe how the night to day transition occurs. It was a lovely experience. I sat in front of the window looking out as the first rays of the sun touched the flower buds in my garden.
4) Soliloquy : Sometimes I just pick up random topics and speak out my views on them to an imaginary audience. It's more or less like giving a speech oblivious to that fact that there are no spectators.
5) Playing piano in the air : I have an ardent wish to learn how to play piano. Currently as I don't find much time I have placed that wish in "To Do Later" list .But often I turn on a piano soundtrack and close my eyes and imitate playing a piano with my fingers dancing playfully in the air. It feels as if I am playing the tune myself.
6) I remember I had to watch Hannibal secretively as my brother complained to my parents saying "Look mom...sis is watching a really "Violent" series". I was banned from watching it. Somehow I completed all the seasons watching it when everybody fell asleep.
And lastly during the time of exams I do all other things (watching movies and TV series, reading thrillers, staring out of the window and day dreaming and so on)but studying when no body's around. That's human psychology I guess. :)