Tone mixups to be avoided at all costs

Ok,well we all know how important getting our tones right are and now CPod has given us a trial tool to play with to get feedback on our tones.Most of the time getting our tones wrong will just lead to confusion...something nonsensical or hard to follow.But sometimes the change in meaning can be disastrous.I thought it might be both fun and useful to compile a list of those homophones or even examples of phrases containing them where the mixup in tones still makes sense but could lead to very embarrasing misunderstandings. I think the first I ever learnt was not to call someones 妈妈 a 马马。I have encountered numerous examples both in the lessons and on the boards,but off the top of my head I can't recall them all and it'd be nice to have a list of some important ones here.So poddies,what do you think are some of the more important ones not to mixup?