Are there any Chinese phrases that have embarrassing meanings if their tones are mispronounced?
These below are not exactly embarassing, but nonetheless funny words that have different meanings when pronounced with different tones.


看書 (read book) kàn shū / 砍樹 (chuck wood) kǎn shù
湯水 (soup) tāng shuǐ / 糖水 (syrup/sweet soup) táng shuǐ
號碼 (number) hào mǎ / 好嗎 (okay?) hǎo ma
大人 (adult) dàrén / 打人 (beat somebody) dǎ rén
火車 (train) huǒchē / 貨車 (truck) huòchē
好帥 (handsome) hǎo shuài / 好衰 (mean) hǎo shuāi
美麗 (beautiful) měilì / 沒理 (unreasonable) méilǐ
妻子 (wife) qīzi / 棋子 (chest piece) qízi 
梨子蛋糕 (pear cake) lí zi dàn gāo / 李子蛋糕 (plum cake) lĭ zi dàn gāo / 栗子蛋糕 (chestnut cake) lì zi dàn gāo
搭便車 (hitchhiking) dā biàn chē / 大便車 (stool vehicle) dà biàn chē / 打扁車 (flatten a car) dă biăn chē
杯子 (cup) bēi zi / 被子 (quilt) bèi zi
禿子 (bald guy) tū zi / 兔子 (rabbit) tù zĭ
消化 (digest) xiāo huà / 笑話 (joke) xiào hua
珠子 (bead) zhū zi / 柱子 (pillar) zhù zi
進攻 (attack) jìn gōng / 進貢 (tribute) jìn gòng
歌星 (singer) gē xīng / 個性 (personality) gè xìng
獅子 (lion) shī zi / 柿子 (persimmon)shì zi
大官 (high official) dà guān / 大罐 (big can or pot) dà guàn
司機 (chauffeur) sī jī / 四季 (four seasons) sì jì
相思 (lovesick) xiāng sī / 相似 (similar) xiāng sì
通信 (send letters) tōng xìn / 痛心 (broken-hearted) tòng xīn
包紙 (wrap) bāo zhĭ / 報紙 (newspaper) bào zhĭ
推銷 (sell) tuī xiāo / 退燒 (reduce fever) tuì shāo
搬家 (move home) bān jiā / 半價 (half price) bàn jià
兵士 (soldier) bīng shì / 病逝 (die with illness) bìng shì
徒弟 (apprentice) tú dì / 土地 (land) tŭ dì
留條 (leave a note) liú tiáo / 柳條 (wicker/willow) liŭ tiáo
研習 (learn) yán xí / 演習 (rehearsal/drill) yăn xí
涼台 (veranda) liáng tái / 兩台 (two sets) liăng tái
零錢 (change money) líng qián / 領錢 (receive money) lĭng qián 
圖畫 (picture) tú huà / 土話 (dialect) tŭ huà 
竹蓆 (bamboo mat) zhú xí / 主席 (chairman) zhŭ xí 
完了 (finished) wán le / 晚了 (late) wăn le 
毒氣 (poisonous gas) dú qì / 賭氣 (pique) dŭ qì 
飛機 (aircraft) fēi jī / 肥雞 (fat chicken) féi jī / 匪機 (bandit plane) fěi jī
支援 (support) zhī yuán / 職員 (staff) zhí yuán / 只願 (only desire) zhĭ yuàn / 志願 (volunteer) zhì yuàn


A few more on the web:

http://www.hellouk.org/forum/index.php?showtopic=90874

http://susanfat.mysinablog.com/index.php?op=ViewArticle&amp;articleId=4444909