not really a worst thing/best thing but one time i was dared to answer my phone while we were doing it...i'm sure the conversation was a little strange
I always hope a telemarketer will call during a sex session...
Telemarketer: are you eating right now?
Me: not yet, but when its my turn, she will let me know.
I used to do telesales. Part of our 'training' included listening to a call whereby a couple in the act were called and didn't hang up the phone...the best part was, they listened to the spiel about insurance first, and then the sort of gasping sounds interrupted the poor telesales guy...
But, on topic:
This one for guys: "This is just like the last time I went bowling!"
and...
"So, have you tried watersports before?"
"I think you broke it"
"So, I spoke to my ex today..."
"Good effort."
"Shabba!" (Not that funny, but I knew someone who thought themselves hilarious for that one)
(In the voice of a young kid) "Are we there yet? Are we there yet?"
Start singing Sic Transit Gloria
"So, if you're free tomorrow, shall we take a trip to the VD clinic?"
...