<p>If you email a former professor just to say hello, tell them what's going on with you, ask how things are going with them, ask what their up to, etc. do you think it's ok to joke around a little bit? (I'm still a student at the college)</p>
<p>Drop by office hours so he can connect a name with a face.</p>
<p>I’ve talked to him a couple times since the class ended in person, and he told me to keep him updated and stop by occasionally. A couple of weeks ago, I ran into him in the hall, and he said hello, asked how I was,etc.</p>
<p>I would talk to him however you would normally talk to him if you stopped by his office hours (erring on the side of more formal side when in doubt, since you can’t always get tone of voice and other cues in an email). If you normally joke around with him, it’s not inappropriate to do so now. If you don’t normally have that type of relationship with him or he isn’t that type of person, then I wouldn’t do it in an email.</p>