in situations like that its hard to turn it around but not impossible , if these people mean anything to you meaning you would like to be freinds with them , just say hey come on guys im shy but dont take the mic , cos its really pissing me off , sometimes you have to make a stand lol ... but to be honest people like that are prob only having a laugh dont take it to personaly ... just try to join in , do the same back lol ... iv been there years ago , you just have to find a little confidence in yourself , its there , its just bringing it out thats hard , but not impossible