SB 7.9.45

yan maithunādi-gṛhamedhi-sukhaṁ hi tucchaṁ
 kaṇḍūyanena karayor iva duḥkha-duḥkham
tṛpyanti neha kṛpaṇā bahu-duḥkha-bhājaḥ
 kaṇḍūtivan manasijaṁ viṣaheta dhīraḥ
Synonyms: 
yat — that which (is meant for material sense gratification); maithuna-ādi — represented by talking of sex, reading sexual literature or enjoying sex life (at home or outside, as in a club); gṛhamedhi-sukham — all types of material happiness based on attachment to family, society, friendship, etc; hi — indeed; tuccham — insignificant; kaṇḍūyanena — with the itching; karayoḥ — of the two hands (to relieve the itching); iva — like; duḥkha-duḥkham — different types of unhappiness (into which one is put after such itching sense gratification); tṛpyanti — become satisfied; na — never; iha — in material sense gratification; kṛpaṇāḥ — the foolish persons; bahu-duḥkha-bhājaḥ — subjected to various types of material unhappiness; kaṇḍūti-vat — if one can learn from such itching; manasi-jam — which is simply a mental concoction (actually there is no happiness); viṣaheta — and tolerates (such itching); dhīraḥ — (he can become) a most perfect, sober person.
Translation: 
Sex life is compared to the rubbing of two hands to relieve an itch. Gṛhamedhis, so-called gṛhasthas who have no spiritual knowledge, think that this itching is the greatest platform of happiness, although actually it is a source of distress. The kṛpaṇas, the fools who are just the opposite of brāhmaṇas, are not satisfied by repeated sensuous enjoyment. Those who are dhīra, however, who are sober and who tolerate this itching, are not subjected to the sufferings of fools and rascals.
Purport: 

Materialists think that sexual indulgence is the greatest happiness in this material world, and therefore they make elaborate plans to satisfy their senses, especially the genitals. This is generally found everywhere, and specifically found in the Western world, where there are regular arrangements to satisfy sex life in different ways. Actually, however, this has not made anyone happy. Even the hippies, who have given up all the materialistic comforts of their fathers and grandfathers, cannot give up the sensational happiness of sex life. Such persons are described here as kṛpaṇas, misers. The human form of life is a great asset, for in this life one can fulfill the goal of existence. Unfortunately, however, because of a lack of education and culture, people are victimized by the false happiness of sex life. Prahlāda Mahārāja therefore advises one not to be misled by this civilization of sense gratification, and especially not by sex life. Rather, one should be sober, avoid sense gratification and be Kṛṣṇa conscious. The lusty person, who is compared to a foolish miser, never gets happiness by sense gratification. The influence of material nature is very difficult to surpass, but as stated by Kṛṣṇa in Bhagavad-gītā (7.14), mām eva ye prapadyante, māyām etāṁ taranti te: if one voluntarily submits to the lotus feet of Kṛṣṇa, he can be saved very easily.

In reference to the low-grade happiness of sex life, Yāmunācārya says in this connection:

yadāvadhi mama cetaḥ kṛṣṇa-padāravinde
 nava-nava-rasa-dhāmanudyata rantum āsīt
tadāvadhi bata nārī-saṅgame smaryamāne
 bhavati mukha-vikāraḥ suṣṭu niṣṭhīvanaṁ ca

“Since I have been engaged in the transcendental loving service of Kṛṣṇa, realizing ever-new pleasure in Him, whenever I think of sex pleasure, I spit at the thought, and my lips curl with distaste.” Yāmunācārya had formerly been a great king who enjoyed sexual happiness in various ways, but since he later engaged himself in the service of the Lord, he enjoyed spiritual bliss and hated to think of sex life. If sexual thoughts came to him, he would spit with disgust.