If i have mono, can laughing too hard rupture my spleen?

Generally, no: The spleen may become mildly to grossly enlarged during the course of having mono. In general, your physician will recommend no "rough physical activity" such as football or skiing. A hearty, robust laugh should not be enough to rupture spleen and it may in fact be good for the healing process. Just be aware, don't let the laughter get you too riled up though.

Possible: Mononucleosis is often associated with an enlarged speen, which is at increased risk of rupture. Cases of rupture are rare, fortunately, and usually associated with more major trauma than laughing, but depending on the size of the spleen, the risk may be significant.