| Jabber away | Talk rapidly or incomprehensibly. | They started jabbering away about file systems and I couldn’t follow their conversation at all. |
| Jack around | Cause trouble for someone, fail to keep promises. | Don’t trust him; he always jacks people around and never follows through with his commitments. |
| Jack in | Quit or give up. | I had to jack my job in because my boss wouldn’t give me a raise. |
| Jack up | Raise a car for mechanical work or increase sharply. | We jacked the car up to change the tire. |
| Jack up | Increase sharply. | They’ve jacked up the price of oil this month. |
| Jam on | Apply or operate something forcefully. | Jack jammed on the brakes when a rabbit ran in front of his car. |
| Jaw away | Talk incessantly without making any sense. | Your focus should be on helping the student, not just jawing away aimlessly. |
| Jazz up | Make something more exciting or attractive. | They jazzed up the show with some new scenes because it was becoming dull. |
| Jerk around | Cause trouble or treat someone badly. | He was jerking us around and wouldn’t give us a straight answer. |
| Jerk around | Behave foolishly or playfully. | They were just jerking around during the lecture instead of paying attention. |
| Jerk off | Waste time on unimportant things. | Stop jerking off and focus on getting your work done. |
| Joke around | Be humorous or playful. | He’s always joking around in class and making everyone laugh. |
| Jot down | Make a quick note. | I jotted down her number on a piece of paper and now I can’t find it. |
| Juice up | Make something more exciting or perform better. | I need to buy some memory to juice up my computer so it runs faster. |
| Jump at | Accept eagerly or enthusiastically. | I’d jump at the chance to go and live in Japan if I had the opportunity. |
| Jump in | Enter a conversation or situation abruptly. | He jumped in and told them exactly what he thought about the matter. |
| Jump off | Start quickly or successfully. | The IPO jumped off successfully on the first day of trading. |
| Jump on | Criticize or attack someone. | Everyone jumped on me when I raised the issue, criticizing my opinion. |
