Since I'm considering making a Loud/Charity page for Animated Couples, I believe we ought to make a list of the hints of romance between them that came up on "Histeria!" Here's what I've got so far.

China
~Right at the start of the "Learn to Speak Chinese" sketch, Loud & Charity are dancing with each other at the party.

Heroes of Truth and Justice
~In the Rosa Parks sketch, Loud & Charity are sharing the same seat on the bus. Additionally, Charity is clearly annoyed by Loud's singing, but even after she tries (unsuccessfully) to get him to stop, she still continues to sit by him. Apparently, she doesn't want to leave him even if he's annoying her.

Any other hints?

Would being next to each other during kid chorus numbers count? It's pretty hard to find hints.

Even though I haven't seen the sketch since H! was on TV, during the Please Watch Our Show song there is a scene where Loud looks at Charity. I'm not 100% sure since it's been a long time since I saw that sketch/song. Although by judging from what I saw on Encyclopedia Histeria's Image page, it looks like it's from that sketch.

Go here http://www.angelfire.com/tv/enhist/images/ and choose the picture titled Loud and Charity appear to share a laugh to see the picture.

On Presidential People during that tea party with Pule and Charity. When Loud joins in he looks right at Charity before playing. It was from the "Raggity Lyndon Johnson" sketch.

OK, I found another hint m'self; it was when I was watching "Return to Rome" yesterday and taking screenshots from it. At the beginning of the Roman Calendar sketch, when Charity shows us the titular calendar, Loud comes in to shout out the names of the ten months listed. Right as he leaves the shot, Charity seems to be smiling at him, as if she's admiring him! Click here to see that.