Haha'd is a similar phrase like Lol'd.
Basically you're laughing like "haha" but to tell people you've laughed you'd say "I just haha'd" or "haha'd".
Person A: Yo bro'! Ma bitch got pregnant!
Pereson B: Haha'd man! I just haha'd! I told ya to wear protection!
*Reads something on a forum"
- Haha'd! That's so funny! Hahahahaha'd!