笑 – Xiao4 – Smile, Laugh
I always say 笑 when I mean to say 小 and vice versa. Their pronunciation is identical, except for the tone. Stupid tone.
The Chinese equivalent of writing “hahahaha” is 哈哈哈哈. Or for more of a giggly laugh, you write “shee shee shee”: 嘻嘻嘻. This one is likely said with your hand over your mouth.