In some cases, you may experience the issue with the Joomla calendar used in JomSocial that will manifest itself in destorted way similar to image bellow
This however, will have to be fixed by the provider of the template that is currently used on your site
Just to make sure, switch to Joomla's default Beez template and see how nicely calendar will be styled.
This happens, because JomSocial does not style the calendar that is used at events. Although it seems that its a jomsocial calendar, because logically it is loaded on jomsocial page, this actually isnt the case. What really happens is that we use native Joomla calendar which is already available in Joomla, with or without JomSocial installed, and this calendar is styled exclusively by Joomla template (hence it working fine with Beez)
That being said, we cant possibly know how to solve styling problems in the template we didn't created, so please, urge your template provider to do it. It should really have to be fixed on their side as every component that use native Joomla calendar will face the same problem.