Accents. After spending time in Tennessee, I came back with a southern drawl. Took me weeks to shake it. Same thing spending just a weekend in Newark. I came back saying "water" like "whaduh", and "auditorium" like "oo-aw-ditorium".

As I child a child I thought it how long it took a taxi or plumber to arrive 'cos my dad always said "It's taking the contagious to get here "

yawns, ice cream cravings, if you see someone scratching do you often feel an itch, like right now on your elbows.

Beware the Skittles Pox

Laughter tends to be contagious, I recall that I was once in a restaurant with a friend and he told me a joke and I burst into loud laughter and could not stop laughing. Everyone in the restaurant began to stare at me at first but it was not long before the entire restaurant was filled laughter.

I was going to say "rhinovirus," but…

I agree with you on the genuine laugh. Right now it seems like we need a rage vaccine too. Not sure if it is contagious, but stupid seems to be spreading at a really fast rate

Puppies,kittens apple pie and a good pork chop!

I think fear of heights is contagious. I have never met so many people with a fear of heights as I have in Louisiana. It's really weird.

Absolutely real laughter. Especially out-of-control laughter. So fun!

Yawns
Laughter (especially "the giggles" )
Communicable Disease <grin>
Menstrual Cycles (this is a myth and I think it's actually been disproved, but "seems" to happen a lot)

Annoyance with trolls like DoucheyDave

Contagious is anything that takes over your body from emotions, diseases, or enthusiasm.

As of late I think it might be stupidity.

If someone else started to eat something I wasn't going to, then I saw it now I'm eating.

Cabin fever. At a certain point in winter... everyone begins to complain about how far away spring is. We’re going through this in Minneapolis these days.

Dance fever. 2 people get up , 4 people get up . F--- it I'm getting up

My first thought is that "Contagious" is a song released in 2001 by the Isley Brothers featuring R. Kelly and Chanté Moore. Then, I realized that might not be what you mean. For me, puns are contagious, and by that, I don't mean that they make me ill, though the effect on others might be less benign.

Herpese

The beat....

Apparently this nasty little rash I have developed.

They say misery loves company. But for me I seem to sense when someone is depressed and will even get a bit depressed myself. Conversely happy people also seem to help my mood. Don’t know if that is contagious. But it’s definitely something that affects me,

Yawns I believe they maybe the most contagious thing on the planet seems I can even catch from my dogs or cats. The second thing I have noticed that is highly contagious is acting goofy(silly) that has the power to disrupt even to most solemn of events.

Certain catchy or interesting tunes. I find my self playing a lot of famous or popular tunes on my guitar by accident as a result. Lol