It depends on what you mean by "bad" While it is not life threatening, it is not exactly the most optimum way to consume fruits. Will you get nutrients and energy from the fruit if eaten after other foods? Yes. Will you get the maximum benifit? No.
Some experts say that the putrification of the fruit sugars when eaten after "regular" or cooked foods containing fats, protein and carbs will cause illness, cancers and a general state of malnourishment, these effects are not instant, nor are they consistant.
Now to an explaination. When you eat fruit BEFORE anything else (10-40 minutes priot) your stomach has a chance to process all of the nutrients, fiber and most importantly simple sugars that fruit contains. Hence getting "maximum" benifit from the fruit's goodness. In contrast, when you eat fruit AFTER other types of foods, you will still reap some of the nutrient benefits, all of the fiber benefits, but very little if not any of the simple sugar benefits. Simple sugars contained in fruit is processed extremely quickly by the stomach... if not allowed to do so, it will ferment and putrify, therefore giving you the indigestion, burps and other discomforts we've all "blamed" on the fruit we just ate. When in retrospect, if you'd have eaten that SAME fruit on an empty stomach 10-40 minutes (depending on the water content of the fruit i.e. 10mins for an apple or an orange and 30-40 mins for a banana or a date) You'd have most definitely had no problems at all and felt energized and satisfied.
Oh man! You just ate that burger for lunch and got back to the office and found a BEAUTIFUL fruit arrangement on the reception desk... Don't touch it! Give a burger at least 3 hours to leave the stomach before you try that melon. If you had a "healthy" tossed green salad for lunch, the same applies, but for a shorter time of say 1.5 hours.
Try this. Eat ALL the fruit you can before your noon lunch... as much as you want. (except dried) Watch your weight and appetite go down, your energy go up, and you general feeling of wellbeing SOAR through the roof. The BEST time to eat fruit is when you first wake up. That insures that there is NOTHING in your stomach to ferment the sugars and that fruit does it's job 100%!!! Yes, you're going to be hungry in less than an hour, but that's because the fruit is processed and GONE into your body and doing it's job.... EAT more... and more. Then continue your day after lunch with normal foods.