like chime in. To come from no where and bud in the coversation like you were the one in i saying something totaly stupid and unrelated to the coversation.
Arrive, especially unexpectedly.
We'll say u'r in a Train saying a joke to friend then a old lady turns and says to u, 'I heard that one in my day' and laughs, what a blow in.
Or someone uninvited rocks up to your party acting like they've being there from the start, look who just blowed in.
Your playing football with u'r mates and 3 guys, nobody knows, starts playing, what blow ins.