another thing i do is, someone will say a comment that is only minimally funny, but I build on it in my head. like today my math tutor made fun of her professor by saying how he is really into super-heros and so he named his kids Clark and Pepper, and I went with that in my head to wearing a cape at home, and inane hilarious imagery of an aging professor jumping onto his podium in class with gusto wearing said cape going "I am not a bird, I am not a plane, I am an INTELLECTUAL"
I don't know, these are things if said out loud that are not funny, anyways, point being, I build little stories in my head that just keep binging off connections even after the joke has been dead for ten minutes, so weird little giggles keep escapign me in little pockets of air, and i'll be like looking down at my desk, torn between trying to articulate my mental image but it's too late, the moment has passed, and aware that everyone is wondering why I am still laughing...