how do I tell>

there is a boy who is 15 at my high school. I’ve know of him since year 8 but he only started talking to me in year nine. he and his friends have a name for me and they all call me it.there is james, leon, nathan, mickey and lee. mickey and james walk home together bcos they live near each other and they pass me while I’m waiting for mydad 2 pick me up andsay the name. the other day they walked beside me and james asked me will you go out with mickey like in a jokey sort of way. I said no and he told him I sed yes but he heards me say no and I knew they were joking.it’s not bullying but it gets on my nerves because I’ve just broken up with my boyfriend and I do like mickey and would go out with him but I don’t want to say yes if it is only a joke. how do I tell when they are joking and when they aren’t??